Condensed Statements of Changes in Shareholder's Equity (USD $) In Millions, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Deficit)	Total Stockholders' Equity
Balance at Dec. 31, 2010 (As previously filed)		$ 2.5	$ 5,921.7	$ 132.3	$ (1,821.3)	$ 4,235.2
Balance (Cumulative effect of changes in accounting) (Accounting Standards Update 2010-26)				41.1	(394.3)	(353.2)
Balance (Cumulative effect of changes in accounting) (Fair value for Guaranteed Minimum Withdrawal Benefits for Life)				(22.3)	(15.9)	(38.2)
Balance (Cumulative effect of changes in accounting) (Actuarial gains (losses) for pension and post-retirement benefit plans)				3.7	(3.7)	0
Balance at Dec. 31, 2010		2.5	5,921.7	154.8	(2,235.2)	3,843.8
Comprehensive Income[Abstract]
Net income (loss)	236.4				236.4	236.4
Net income (loss) at Jan. 01, 2011 (As previously filed)	489.3
Other comprehensive income, after tax	110.9			110.9		110.9
Other comprehensive income (loss), after tax	347.3					347.3
Contribution of capital			44.0
Employee related benefits			0.7			0.7
Balance at Sep. 30, 2011		2.5	5,966.4	265.7	(1,998.8)	4,235.8
Balance at Dec. 31, 2011	4,136.1	2.5	5,971.6	245.1	(2,083.1)	4,136.1
Comprehensive Income[Abstract]
Net income (loss)	(50.6)				(50.6)	(50.6)
Net income (loss) at Jan. 01, 2012 (As previously filed)	(76.8)
Other comprehensive income, after tax	192.9			192.9		192.9
Other comprehensive income (loss), after tax	142.3					142.3
Distribution of capital			(250.0)
Employee related benefits			33.7			33.7
Balance at Sep. 30, 2012	$ 4,062.1	$ 2.5	$ 5,755.3	$ 438.0	$ (2,133.7)	$ 4,062.1