v3.7.0.1
Marketable Securities (Summary of Available-for-Sale Securities Held) (Details) - USD ($)
$ in Millions
Mar. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Debt Securities, Amortized Cost Basis $ 789 $ 435
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax (1) (2)
Available-for-sale Securities, Debt Securities 788 433
Available-for-sale Equity Securities, Amortized Cost Basis 0 0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax 1 1
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax 0 0
Available-for-sale Securities, Equity Securities 1 1
Available-for-sale Securities, Amortized Cost Basis 789 435
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 1 1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax (1) (2)
Available-for-sale Securities 789 434
Commercial Paper [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Debt Securities, Amortized Cost Basis 38 114
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax 0 0
Available-for-sale Securities, Debt Securities 38 114
Corporate Bond Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Debt Securities, Amortized Cost Basis 387 124
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax 0 (1)
Available-for-sale Securities, Debt Securities 387 123
Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Debt Securities, Amortized Cost Basis 15 91
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax 0 0
Available-for-sale Securities, Debt Securities 15 91
US Government Agencies Debt Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Debt Securities, Amortized Cost Basis 7 28
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax 0 0
Available-for-sale Securities, Debt Securities 7 28
Foreign Government Debt Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Debt Securities, Amortized Cost Basis 331 73
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax (1) (1)
Available-for-sale Securities, Debt Securities 330 72
Certificates of Deposit [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Debt Securities, Amortized Cost Basis 11 5
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax 0 0
Available-for-sale Securities, Debt Securities $ 11 $ 5