Investments in Unconsolidated Affiliates (Symetra) (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended
	Feb. 01, 2016	Feb. 01, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2016
Investments in unconsolidated affiliates
Unrealized gains (losses) on investments			$ 50.8	$ (230.1)
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax			44.3	(195.7)
Sales of common equity securities			$ 17.7	767.5
Common shares, par value per share (in dollars per share)			$ 1.00			$ 1.00
Net realized and unrealized investment gains			$ 51.3	29.5
Symetra
Investments in unconsolidated affiliates
Unrealized gains (losses) on investments					$ 258.8
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax					$ 241.1
Sales of common equity securities	$ 658.0
Common shares, par value per share (in dollars per share)	$ 32.00	$ 32.00
Net realized and unrealized investment gains				4.7
Symetra
Investments in unconsolidated affiliates
Common Stock, Dividends, Per Share, Cash Paid		$ 0.50
Sales of common equity securities				$ 658.0