Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Net income (loss)	$ 325.4	$ 320.3	$ 377.9
Other comprehensive income (loss), before tax:
Unrealized gains/losses on securities	408.7	483.8	465.6
Other-than-temporary impairments	10.6	21.3	(12.7)
Pension and other post-employment benefit liability	(2.2)	7.6	(1.4)
Other comprehensive income (loss), before tax	417.1	512.7	451.5
Income tax benefit (expense) related to items of other comprehensive income (loss)	(141.6)	(155.7)	(77.3)
Other comprehensive income (loss), after tax	275.5	357.0	374.2
Comprehensive income (loss)	$ 600.9	$ 677.3	$ 752.1