Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net income	$ 1,276	$ 1,147	$ 1,231
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of business	(270)	0	0
Depreciation	354	328	309
Amortization	93	121	117
Stock-based compensation	109	98	92
Net realized capital gains	(146)	(20)	(22)
(Benefit) provision for deferred income taxes	(2)	(64)	42
Provision for doubtful accounts	61	32	37
Changes in operating assets and liabilities, net of effect of businesses acquired and dispositions:
Receivables	(180)	(264)	(251)
Other assets	(872)	(952)	(330)
Benefits payable	501	582	109
Other liabilities	(129)	413	313
Unearned revenues	3	155	(24)
Other	70	42	93
Net cash provided by operating activities	868	1,618	1,716
Cash flows from investing activities
Acquisitions, net of cash acquired	(38)	(18)	(187)
Proceeds from sale of business	1,061	72	34
Purchases of property and equipment	(523)	(528)	(441)
Proceeds from sales of property and equipment	1	0	4
Purchases of investment securities	(6,739)	(2,883)	(3,261)
Maturities of investment securities	1,065	885	1,077
Proceeds from sales of investment securities	5,493	2,409	1,592
Net cash provided by (used in) investing activities	320	(63)	(1,182)
Cash flows from financing activities
Receipts (withdrawals) from contract deposits, net	(296)	(919)	(150)
Proceeds from issuance of senior notes, net	0	1,733	0
Proceeds from issuance of commercial paper, net	298	0	0
Repayment of long-term debt	0	(500)	0
Common stock repurchases	(385)	(872)	(531)
Dividends paid	(172)	(172)	(168)
Excess tax benefit from stock-based compensation	15	12	8
Change in book overdraft	(33)	(69)	79
Proceeds from stock option exercises and other, net	21	29	60
Net cash used in financing activities	(552)	(758)	(702)
Increase (decrease) in cash and cash equivalents	636	797	(168)
Cash and cash equivalents at beginning of year	1,935	1,138	1,306
Cash and cash equivalents at end of year	2,571	1,935	1,138
Supplemental cash flow disclosures:
Interest payments	187	143	146
Income tax payments, net	1,179	1,030	734
Details of businesses acquired in purchase transactions:
Fair value of assets acquired, net of cash acquired	38	18	196
Less: Fair value of liabilities assumed	0	0	(9)
Cash paid for acquired businesses, net of cash acquired	$ 38	$ 18	$ 187