Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 630.9	$ 656.2	$ 2,063.0	$ 2,341.5
Other comprehensive (loss) income, net of tax:
Change in net unrealized gains/losses on investments	(133.3)	16.3	151.6	(327.0)
Change in non-credit component of other-than-temporary impairment losses on investments	(3.3)	(0.6)	(3.3)	1.6
Change in net unrealized gains/losses on cash flow hedges	(5.9)	0.7	(4.4)	2.2
Change in net periodic pension and postretirement costs	3.0	4.8	8.9	18.6
Foreign currency translation adjustments	(2.4)	1.2	(2.9)	0.7
Other comprehensive (loss) income	(141.9)	22.4	149.9	(303.9)
Total comprehensive income	$ 489.0	$ 678.6	$ 2,212.9	$ 2,037.6