Schedule I - Parent Company Financial Information (Condensed Statements of Cash Flows) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 1,716	$ 1,923	$ 2,079
Cash flows from investing activities:
Acquisitions	(187)	(1,235)	(226)
Purchases of investment securities	(3,261)	(3,221)	(3,678)
Proceeds from sale of investment securities	1,592	1,404	1,259
Maturities of investment securities	1,077	1,497	1,623
Purchases of property and equipment, net	(441)	(410)	(346)
Net cash used in investing activities	(1,182)	(1,965)	(1,358)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	0	990	0
Change in book overdraft	79	18	(103)
Common stock repurchases	(531)	(518)	(541)
Dividends paid	(168)	(165)	(82)
Tax benefit from stock-based compensation	8	22	15
Proceeds from stock option exercises and other	60	57	72
Net cash (used in) provided by financing activities	(702)	(29)	(1,017)
Increase (decrease) in cash and cash equivalents	(168)	(71)	(296)
Cash and cash equivalents at beginning of year	1,306	1,377	1,673
Cash and cash equivalents at end of year	1,138	1,306	1,377
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	1,554	1,611	1,106
Cash flows from investing activities:
Acquisitions	0	(1,235)	(223)
Capital contributions to operating subsidiaries	(521)	(629)	(214)
Purchases of investment securities	(320)	(338)	(632)
Proceeds from sale of investment securities	35	127	10
Maturities of investment securities	104	316	548
Purchases of property and equipment, net	(223)	(284)	(225)
Net cash used in investing activities	(925)	(2,043)	(736)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	0	990	0
Change in book overdraft	7	7	(21)
Common stock repurchases	(531)	(518)	(541)
Dividends paid	(168)	(165)	(82)
Tax benefit from stock-based compensation	8	22	15
Proceeds from stock option exercises and other	65	60	132
Net cash (used in) provided by financing activities	(619)	396	(497)
Increase (decrease) in cash and cash equivalents	10	(36)	(127)
Cash and cash equivalents at beginning of year	151	187	314
Cash and cash equivalents at end of year	$ 161	$ 151	$ 187