Debt (Senior USD Notes) (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2017 |
Jun. 25, 2015 |
|
| Debt Instrument [Line Items] | ||
| Document Period End Date | Mar. 31, 2017 | |
| Long-term Debt | $ 498.3 | |
| Debt Instrument, Face Amount | $ 500.0 | |
| Series A Notes [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt Instrument, Face Amount | $ 150.0 | |
| Debt Instrument, Interest Rate, Stated Percentage | 2.83% | |
| Debt Instrument, Maturity Date | Jun. 25, 2022 | |
| Series B Notes [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt Instrument, Face Amount | $ 200.0 | |
| Debt Instrument, Interest Rate, Stated Percentage | 3.08% | |
| Debt Instrument, Maturity Date | Jun. 25, 2025 | |
| Series C Notes [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt Instrument, Face Amount | $ 150.0 | |
| Debt Instrument, Interest Rate, Stated Percentage | 3.18% | |
| Debt Instrument, Maturity Date | Jun. 25, 2027 |