v3.7.0.1
Marketable Securities (Available-for-Sale Securities by Classification in Balance Sheet) (Details) - USD ($)
$ in Millions
Mar. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Debt Securities $ 788 $ 433
Available-for-sale Securities 789 434
Cash and Cash Equivalents [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Debt Securities 57 120
Marketable Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Debt Securities $ 732 $ 314