Investments in Unconsolidated Affiliates (Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments in and Advances to Affiliates
Total investments	$ 5,334.8				$ 4,271.1					$ 5,334.8	$ 4,271.1
Total assets	6,544.7				10,282.6					6,544.7	10,282.6
Long-term debt	285.9				337.6					285.9	337.6
Total liabilities	2,807.5				5,914.6					2,807.5	5,914.6
Common shareholders’ equity	3,737.2				4,368.0					3,737.2	4,368.0
Earned insurance premiums										1,114.0	1,188.2	$ 1,185.0
Net investment income										86.8	60.8	59.5
(Loss) revenues (including realized gains and losses)	268.2	$ 365.0	$ 358.2	$ 369.3	602.6	$ 296.1	$ 368.7	$ 354.3		1,360.7	1,621.7	1,411.1
Expenses	$ 335.0	$ 345.0	$ 360.3	$ 360.8	$ 356.3	383.0	$ 373.8	$ 351.3		1,401.1	1,464.4	1,440.5
Net income										419.8	279.5	290.0
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest										$ 558.1	$ 197.2	207.3
Symetra
Investments in and Advances to Affiliates
Total investments						32,409.2			$ 32,409.2
Separate account assets						885.9			885.9
Total assets						34,962.8			34,962.8
Policyholder liabilities						29,492.0			29,492.0
Long-term debt						697.5			697.5
Separate account liabilities						885.9			885.9
Total liabilities						31,836.7			31,836.7
Common shareholders’ equity						$ 3,126.1			3,126.1
Earned insurance premiums									539.3			629.1
Net investment income									994.3			1,320.5
(Loss) revenues (including realized gains and losses)									1,605.9			2,182.4
Liability for Future Policy Benefits, Period Expense (Income)									1,143.7			1,399.7
Expenses									1,543.6			1,882.5
Net income									89.6			254.4
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest									$ (234.1)			$ 397.0