Fair Value Measurements (Debt Instruments) (Details) $ in Millions |
Dec. 31, 2017
USD ($)
|
---|---|
$750.0 million fixed rate notes due September 2022, stated rate of 3.00% | |
Debt Instrument, Fair Value Disclosure | $ 764.9 |
Seven Hundred Fifty Million Fixed Rate Notes Due March Two Thousand Twenty Five, Interest Equal To Three Point Zero Percent [Member] [Member] | |
Debt Instrument, Fair Value Disclosure | 758.2 |
Seven Hundred Fifty Million Fixed Rate Notes Due September Two Thousand Forty Three, Interest Equal To Five Point Three Percent [Member] | |
Debt Instrument, Fair Value Disclosure | $ 960.0 |