Schedule I - Parent Company Financial Information (Condensed Statements of Cash Flows) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 868	$ 1,618	$ 1,716
Cash flows from investing activities:
Proceeds from sale of business	1,061	72	34
Acquisitions	(38)	(18)	(187)
Purchases of investment securities	(6,739)	(2,883)	(3,261)
Proceeds from sale of investment securities	5,493	2,409	1,592
Maturities of investment securities	1,065	885	1,077
Purchases of property and equipment, net	(523)	(528)	(441)
Net cash provided by (used in) investing activities	320	(63)	(1,182)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	0	1,733	0
Proceeds from issuance of commercial paper, net	298	0	0
Repayments of Long-term Debt	0	(500)	0
Change in book overdraft	(33)	(69)	79
Common stock repurchases	(385)	(872)	(531)
Dividends paid	(172)	(172)	(168)
Tax benefit from stock-based compensation	15	12	8
Proceeds from stock option exercises and other	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
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	953	1,499	1,554
Cash flows from investing activities:
Proceeds from sale of business	1,055	0	0
Acquisitions	0	0	0
Capital contributions to operating subsidiaries	(833)	(442)	(521)
Purchases of investment securities	(507)	(629)	(320)
Proceeds from sale of investment securities	18	606	35
Maturities of investment securities	108	149	104
Purchases of property and equipment, net	(378)	(380)	(223)
Net cash provided by (used in) investing activities	(537)	(696)	(925)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	0	1,733	0
Proceeds from issuance of commercial paper, net	298	0	0
Repayments of Long-term Debt	0	(500)	0
Change in book overdraft	(16)	(5)	7
Common stock repurchases	(385)	(872)	(531)
Dividends paid	(172)	(172)	(168)
Tax benefit from stock-based compensation	15	12	8
Proceeds from stock option exercises and other	22	51	65
Net cash used in financing activities	(238)	247	(619)
Increase (decrease) in cash and cash equivalents	178	1,050	10
Cash and cash equivalents at beginning of year	1,211	161	151
Cash and cash equivalents at end of year	$ 1,389	$ 1,211	$ 161