Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Income (loss) before income taxes	$ 112.8	$ 58.5	$ 219.7	$ 276.7
Tax rate	35.00%	35.00%	35.00%	35.00%
Income tax expense (benefit) at federal statutory rate	39.5	20.4	76.9	96.8
Dividends received deduction	(6.3)	(6.0)	(11.6)	(12.0)
Valuation allowance	1.9	6.0	1.9	10.0
IRS audit adjustment	0	0	(0.3)	(0.3)
Other	0.8	0.2	0.8	0.3
Income tax expense (benefit)	35.9	20.6	67.7	94.8
Increase (decrease) in valuation allowance	0	0	0	0
Tax valuation allowance allocated to Net income (loss)
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Valuation allowance, deferred tax assets	64.7		64.7		62.8
Increase (decrease) in valuation allowance	1.9	6.0	1.9	10.0
Tax valuation allowance allocated to Other comprehensive income
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Valuation allowance, deferred tax assets	(53.6)		(53.6)		(51.7)
Increase (decrease) in valuation allowance	(1.9)	(6.0)	(1.9)	(10.0)
Operating loss carryforwards | Foreign tax credits
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Valuation allowance, deferred tax assets	$ 11.1		$ 11.1		$ 11.1