Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 701.0	$ 885.2
Other comprehensive income, net of tax:
Change in net unrealized gains/losses on investments	140.3	34.5
Change in non-credit component of other-than-temporary impairment losses on investments	0.5	2.2
Change in net unrealized gains/losses on cash flow hedges	0.7	0.7
Change in net periodic pension and postretirement costs	2.9	6.8
Foreign currency translation adjustment, net of tax benefit of $0.0 and $0.5, respectively	(0.2)	(0.8)
Other comprehensive income	144.2	43.4
Total comprehensive income	$ 845.2	$ 928.6