Investment Securities (Net Realized and Unrealized Gains (Losses) After Tax) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Net change in pre-tax unrealized gains (losses) on investments in unconsolidated affiliates	$ 81.2	$ (106.4)	$ 62.8
Income taxes	(5.9)	8.3	(5.1)
Net change in unrealized gains (losses) on investments in unconsolidated affiliates, after tax	75.3	(98.1)	57.7
Net realized and unrealized foreign currency (losses) gains on investments through OCI	(274.3)	11.3	95.5
Total investment (losses) gains through accumulated other comprehensive income	(199.0)	(86.8)	153.2
Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	214.2	139.8	91.4
Total investment gains recorded during the period, after-tax	$ 15.2	$ 53.0	$ 244.6