Condensed Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Statement of Other Comprehensive Income [Abstract]
Net income (loss)	$ 192.2	$ 122.3	$ (50.6)	$ 236.4
Other comprehensive income (loss), before tax:
Unrealized gains/losses on securities	266.8	121.7	469.1	47.1
Other-than-temporary impairments	6.2	(151.9)	13.3	30.5
Pension and other post-employment benefit liability	(0.1)	(0.1)	(0.2)	(0.2)
Other comprehensive income (loss), before tax	272.9	(30.3)	482.2	77.4
Income tax benefit (expense) related to items of other comprehensive income (loss)	(200.5)	66.3	(289.3)	33.5
Other comprehensive income (loss), after tax	72.4	36.0	192.9	110.9
Comprehensive income (loss)	$ 264.6	$ 158.3	$ 142.3	$ 347.3