Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Other Comprehensive Income [Abstract]
Net income	$ 656.2	$ 691.2	$ 2,341.5	$ 2,191.3
Other comprehensive income (loss), net of tax:
Change in net unrealized gains/losses on investments	16.3	168.3	(327.0)	248.5
Change in non-credit component of other-than-temporary impairment losses on investments	(0.6)	0	1.6	4.4
Change in net unrealized gains/losses on cash flow hedges	0.7	(1.0)	2.2	(0.6)
Change in net periodic pension and postretirement costs	4.8	6.9	18.6	19.9
Foreign currency translation adjustments	1.2	0.5	0.7	(0.2)
Other comprehensive income (loss)	22.4	174.7	(303.9)	272.0
Total comprehensive income	$ 678.6	$ 865.9	$ 2,037.6	$ 2,463.3