Investments in Unconsolidated Affiliates (Symetra) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2011
Investments in unconsolidated affiliates
Revenues	$ 334.7	$ 323.2	$ 1,130.1	$ 1,048.5
Total expenses	429.3	358.7	1,233.3	1,011.8
Pre-tax (loss) income	(94.6)	(35.5)	(103.2)	36.7
Net income	$ (74.9)	40.1	5.5	235.1
Symetra
Investments in unconsolidated affiliates
Dividends	$ 0.50
Revenues			$ 1,605.9	1,601.6
Stock Repurchased and Retired During Period, Value	513,500
Shares of Symetra Financial Corporation owned (in shares)	20,562,379		20,562,379			20,048,879
Ownership interest (as a percent)	17.70%		17.70%			17.31%
Equity Method Investments Fair Value Per Share							$ 15
Term of amortization (in years)					30 years
Weight Average Years Remaining			28 years
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 160.8		$ 160.8			$ 170.4
Total expenses			1,543.6	1,387.0
Pre-tax (loss) income			62.3	214.6
Net income			89.6	186.8
Common Stock | Symetra
Investments in unconsolidated affiliates
Proceeds from Equity Method Investment, Dividends or Distributions	$ 12.5	2.0	$ 16.9	6.0
Fair value of investment							$ 261.0
Share Price	$ 31.64		$ 31.64
equity in earnings of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in earnings	$ 0.6	0.7	$ 2.0	2.1
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	32.6		32.6			36.4
Net unrealized gains (losses) of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in net unrealized losses	2.6	$ 2.9	8.1	$ 8.7
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 128.2		$ 128.2			$ 134.0
Expected [Member] | Symetra
Investments in unconsolidated affiliates
Dividends Payable, Amount Per Share	$ 32.00		$ 32.00
Special Dividend [Member] | Common Stock | Symetra
Investments in unconsolidated affiliates
Proceeds from Equity Method Investment, Dividends or Distributions	$ (10.3)