Investment Securities (Net Realized and Unrealized Gains (Losses) After Tax) (Details) - USD ($) $ in Millions	10 Months Ended	12 Months Ended
	Nov. 05, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments in and Advances to Affiliates [Line Items]
Net change in pre-tax unrealized gains (losses) on investments in unconsolidated affiliates		$ (39.2)	$ 81.2	$ (106.4)
Income tax benefit (expense)		2.9	(5.9)	8.3
Net change in unrealized (losses) gains on investments in unconsolidated affiliates, after tax		(36.3)	75.3	(98.1)
Net change in unrealized (losses) gains on investments in unconsolidated affiliates, after tax		(34.9)	75.3	(98.1)
Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax		190.2	60.5	121.1
Total investment gains recorded during the period, after-tax		155.3	135.8	23.0
Symetra
Investments in and Advances to Affiliates [Line Items]
Net change in pre-tax unrealized gains (losses) on investments in unconsolidated affiliates	$ (39.2)		81.2	(106.4)
Net change in unrealized (losses) gains on investments in unconsolidated affiliates, after tax		(34.9)	75.3	(98.1)
Reversal of accumulated other comprehensive income related to change in accounting for the investment in Symetra		$ 1.4	$ 0.0	$ 0.0