Derivatives (Forward Contract Collateral) (Details) In Millions, unless otherwise specified	Mar. 31, 2015 USD ($)	Mar. 31, 2015 JPY (¥)	Dec. 31, 2014 USD ($)	Dec. 31, 2014 JPY (¥)	Mar. 31, 2015 Forward Contracts USD ($) Rating	Mar. 31, 2015 Forward Contracts SEK	Dec. 31, 2014 Forward Contracts USD ($)	Mar. 31, 2015 Interest Rate Cap Rating	Mar. 31, 2015 Standard & Poor's, A Rating Forward Contracts Barclays USD ($)	Dec. 31, 2014 Standard & Poor's, A Rating Forward Contracts Barclays USD ($)	Mar. 31, 2015 Standard & Poor's, A Rating Forward Contracts Deutsche Bank USD ($)	Dec. 31, 2014 Standard & Poor's, A Rating Forward Contracts Deutsche Bank USD ($)	Mar. 31, 2015 Standard & Poor's, A Rating Forward Contracts Goldman Sachs USD ($)	Dec. 31, 2014 Standard & Poor's, A Rating Forward Contracts Goldman Sachs USD ($)	Mar. 31, 2015 Standard & Poor's, A plus Forward Contracts JP Morgan USD ($)	Dec. 31, 2014 Standard & Poor's, A plus Forward Contracts JP Morgan USD ($)	Mar. 31, 2015 Standard & Poor's, AA- Rating Forward Contracts HSBC USD ($)	Dec. 31, 2014 Standard & Poor's, AA- Rating Forward Contracts HSBC USD ($)	Mar. 31, 2015 Standard & Poor's, AA- Rating Forward Contracts Royal Bank of Canada USD ($)	Dec. 31, 2014 Standard & Poor's, AA- Rating Forward Contracts Royal Bank of Canada USD ($)
Derivative [Line Items]
Notional amount	$ 1,000.0	¥ 117,800.0	$ 1,100.0	¥ 134,200.0	$ 56.5	489.3	$ 33.1		$ 6.3	$ 2.1	$ 4.4	$ 0	$ 10.9	$ 8.7	$ 7.3	$ 5.7	$ 21.7	$ 11.2	$ 5.9	$ 5.4
Carrying Value					$ 0		$ 0		$ 0	$ 0	$ 0.1	$ 0	$ 0	$ 0	$ (0.1)	$ 0	$ 0	$ 0	$ 0	$ 0
S and P Credit Ratings					23	23		23