Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income	$ 2,448	$ 614	$ 1,276
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of business	0	0	(270)
Depreciation	410	388	354
Amortization	75	77	93
Stock-based compensation	157	115	109
Net realized capital gains	(14)	(96)	(146)
Provision (benefit) for deferred income taxes	132	(71)	(2)
Provision for doubtful accounts	20	39	61
Changes in operating assets and liabilities, net of effect of businesses acquired and dispositions:
Receivables	406	(158)	(180)
Other assets	(582)	426	(872)
Benefits payable	105	(413)	501
Other liabilities	641	937	(129)
Unearned revenues	98	(84)	3
Other	155	162	70
Net cash provided by operating activities	4,051	1,936	868
Cash flows from investing activities
Acquisitions, net of cash acquired	(31)	(7)	(38)
Proceeds from sale of business	0	0	1,061
Purchases of property and equipment	(526)	(527)	(523)
Proceeds from sales of property and equipment	2	0	1
Purchases of investment securities	(6,265)	(6,566)	(6,739)
Maturities of investment securities	1,111	1,426	1,065
Proceeds from sales of investment securities	2,768	4,312	5,493
Net cash (used in) provided by investing activities	(2,941)	(1,362)	320
Cash flows from financing activities
Receipts (withdrawals) from contract deposits, net	1,823	1,093	(296)
Proceeds from issuance of senior notes, net	1,779	0	0
(Repayments) proceeds from issuance of commercial paper, net	(153)	(2)	298
Repayment of long-term debt	(800)	0	0
Common stock repurchases	(3,365)	(104)	(385)
Dividends paid	(220)	(177)	(172)
Excess tax benefit from stock-based compensation	0	0	15
Change in book overdraft	(71)	(89)	(33)
Proceeds from stock option exercises and other, net	62	11	21
Net cash (used in) provided by financing activities	(945)	732	(552)
Increase in cash and cash equivalents	165	1,306	636
Cash and cash equivalents at beginning of year	3,877	2,571	1,935
Cash and cash equivalents at end of year	4,042	3,877	2,571
Supplemental cash flow disclosures:
Interest payments	216	185	187
Income tax payments, net	1,498	916	1,179
Details of businesses acquired in purchase transactions:
Fair value of assets acquired, net of cash acquired	31	7	38
Less: Fair value of liabilities assumed	0	0	0
Cash paid for acquired businesses, net of cash acquired	$ 31	$ 7	$ 38