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Investments in Unconsolidated Affiliates (Symetra) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended				9 Months Ended
	Feb. 01, 2016	Sep. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2011
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		$ 0.0			$ 3.9	$ 0.0	$ 18.0
Unrealized gains (losses) on investments		18.1			(36.3)	(186.4)	(80.3)
Revenues		365.0			296.1	1,092.5	1,019.1
Total expenses		345.0			383.0	1,066.1	1,108.1
Pre-tax (loss) income		20.0			(86.9)	26.4	(89.0)
Net income		88.6			(74.9)	470.4	5.5
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax		$ 15.4			(28.4)	(164.2)	(57.7)
Sales of common equity securities						$ 961.1	370.6
Common shares, par value per share (in dollars per share)		$ 1.00		$ 1.00		$ 1.00
Net realized and unrealized investment gains (losses)		$ 26.4			(43.9)	$ 84.0	(33.9)
Symetra
Investments in unconsolidated affiliates
Unrealized gains (losses) on investments				$ 258.8
Dividends Payable, Amount Per Share	$ 32.00
Equity Method Investments Fair Value Per Share								$ 15
Term of amortization (in years)						30 years
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity					160.8		160.8
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
Net realized and unrealized investment gains (losses)			$ 4.7
Common Stock | Symetra
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax					4.2		17.5
Proceeds from Equity Method Investment, Dividends or Distributions					12.5		16.9
equity in earnings of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in earnings					0.6		2.0
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity					32.6		32.6
Net unrealized gains (losses) of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in net unrealized losses					2.6		8.1
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity					128.2		128.2
Amortization of common share basis difference | Common Stock | Symetra
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax					0.7		2.1
Special Dividend [Member] | Common Stock | Symetra
Investments in unconsolidated affiliates
Proceeds from Equity Method Investment, Dividends or Distributions					$ 10.3		$ 10.3

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