Investments in Unconsolidated Affiliates (Symetra) (Details) - USD ($)		3 Months Ended					6 Months Ended		10 Months Ended	12 Months Ended
	Feb. 01, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015	Nov. 05, 2015	Dec. 31, 2015	Dec. 31, 2011
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		$ 0			$ 6,800,000		$ 0	$ 14,100,000
Unrealized gains (losses) on investments		25,600,000			(59,100,000)		(204,500,000)	(43,900,000)
Revenues		358,200,000			368,700,000		727,500,000	723,000,000
Total expenses		360,300,000			373,800,000		721,100,000	725,100,000
Pre-tax (loss) income		(2,100,000)			(5,100,000)		6,400,000	(2,100,000)
Net income		362,500,000			3,400,000		381,800,000	80,400,000
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax		$ 16,100,000			(41,800,000)		(179,600,000)	(29,200,000)
Sales of common equity securities							$ 851,300,000	306,800,000
Common shares, par value per share (in dollars per share)		$ 1.00		$ 1.00			$ 1.00			$ 1.00
Net realized and unrealized investment gains (losses)		$ 28,100,000			(15,000,000)		$ 57,600,000	$ 10,000,000
Symetra
Investments in unconsolidated affiliates
Unrealized gains (losses) on investments				$ 258,800,000
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					164,100,000			$ 164,100,000
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax				$ 241,100,000
Sales of common equity securities	$ 658,000,000
Common shares, par value per share (in dollars per share)	$ 32.00
Net realized and unrealized investment gains (losses)			$ 4,700,000.00
Common Stock | Symetra
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax					6,100,000			13,300,000
Proceeds from Equity Method Investment, Dividends or Distributions					2,200,000	$ 2,200,000		4,400,000	$ 4,400,000
equity in earnings of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in earnings					700,000			1,400,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity					33,000,000			33,000,000
Net unrealized gains (losses) of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in net unrealized losses					2,700,000			5,500,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity					131,100,000			$ 131,100,000
Expected [Member] | Symetra
Investments in unconsolidated affiliates
Dividends Payable, Amount Per Share			$ 32.00
Amortization of common share basis difference | Common Stock | Symetra
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax					$ 700,000					$ 1,400,000