Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities
Net income	$ 1,222	$ 1,419	$ 1,099
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	338	303	263
Stock-based compensation	82	67	63
Net realized capital gains	(33)	(11)	(6)
(Benefit) provision for deferred income taxes	(80)	22	(199)
Provision for doubtful accounts	26	31	19
Changes in operating assets and liabilities, net of effect of businesses acquired:
Receivables	326	(106)	(46)
Other assets	(253)	(183)	81
Benefits payable	(41)	256	247
Other liabilities	300	194	722
Unearned revenues	(43)	26	(46)
Other	79	61	45
Net cash provided by operating activities	1,923	2,079	2,242
Cash flows from investing activities
Acquisitions, net of cash acquired	(1,235)	(226)	(833)
Purchases of property and equipment	(410)	(346)	(222)
Proceeds from sales of property and equipment	0	10	0
Purchases of investment securities	(3,221)	(3,678)	(4,589)
Maturities of investment securities	1,497	1,623	1,821
Proceeds from sales of investment securities	1,404	1,259	2,012
Net cash used in investing activities	(1,965)	(1,358)	(1,811)
Cash flows from financing activities
Receipts (withdrawals) from contract deposits, net	(397)	(378)	(237)
Proceeds from issuance of senior notes, net	990	0	0
Repayment of long-term debt	(36)	0	0
Common stock repurchases	(518)	(541)	(108)
Dividends paid	(165)	(82)	0
Excess tax benefit from stock-based compensation	22	15	2
Change in book overdraft	18	(103)	35
Proceeds from stock option exercises and other, net	57	72	(63)
Net cash provided by (used in) financing activities	(29)	(1,017)	(371)
(Decrease) increase in cash and cash equivalents	(71)	(296)	60
Cash and cash equivalents at beginning of year	1,377	1,673	1,613
Cash and cash equivalents at end of year	1,306	1,377	1,673
Supplemental cash flow disclosures:
Interest payments	110	114	112
Income tax payments, net	745	874	785
Details of businesses acquired in purchase transactions:
Fair value of assets acquired, net of cash acquired	1,535	266	1,044
Less: Fair value of liabilities assumed	(300)	(40)	(211)
Cash paid for acquired businesses, net of cash acquired	$ 1,235	$ 226	$ 833