Consolidated Statements Of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues
Premiums	$ 20,951.3	$ 18,988.9
Administrative fees	1,363.2	1,311.0
Other revenue	5.0	9.5
Total operating revenue	22,319.5	20,309.4
Net investment income	207.2	171.1
Net realized gains (losses) on financial instruments	7.3	(125.1)
Other-than-temporary impairment losses on investments:
Total other-than-temporary impairment losses on investments	(9.6)	(85.2)
Portion of other-than-temporary impairment losses recognized in other comprehensive income	1.5	18.3
Other-than-temporary impairment losses recognized in income	(8.1)	(66.9)
Total revenues	22,525.9	20,288.5
Expenses
Benefit expense	17,542.8	15,538.8
Selling, general and administrative expense:
Selling expense	348.6	349.9
General and administrative expense	2,842.7	2,850.3
Total selling, general and administrative expense	3,191.3	3,200.2
Interest expense	235.0	187.1
Amortization of other intangible assets	41.8	50.4
Total expenses	21,010.9	18,976.5
Income before income tax expense	1,515.0	1,312.0
Income tax expense	505.1	609.0
Net income	$ 1,009.9	$ 703.0
Net income per share
Basic net income per share	$ 3.82	$ 2.69
Diluted net income per share	3.73	2.63
Dividends per share	$ 0.65	$ 0.65