Schedule I - Parent Company Financial Information (Condensed Statements of Cash Flows) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 1,923	$ 2,079	$ 2,242
Cash flows from investing activities:
Acquisitions	(1,235)	(226)	(833)
Purchases of investment securities	(3,221)	(3,678)	(4,589)
Proceeds from sale of investment securities	1,404	1,259	2,012
Maturities of investment securities	1,497	1,623	1,821
Purchases of property and equipment, net	(410)	(346)	(222)
Net cash used in investing activities	(1,965)	(1,358)	(1,811)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	990	0	0
Change in book overdraft	18	(103)	35
Common stock repurchases	(518)	(541)	(108)
Dividends paid	(165)	(82)	0
Tax benefit from stock-based compensation	22	15	2
Proceeds from stock option exercises and other	57	72	(63)
Net cash provided by (used in) financing activities	(29)	(1,017)	(371)
Decrease 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
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	1,611	1,106	1,219
Cash flows from investing activities:
Acquisitions	(1,235)	(223)	(840)
Purchases of investment securities	(338)	(632)	(633)
Proceeds from sale of investment securities	127	10	16
Maturities of investment securities	316	548	698
Purchases of property and equipment, net	(284)	(225)	(166)
Capital contributions to operating subsidiaries	(629)	(214)	(230)
Net cash used in investing activities	(2,043)	(736)	(1,155)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	990	0	0
Change in book overdraft	7	(21)	2
Common stock repurchases	(518)	(541)	(108)
Dividends paid	(165)	(82)	0
Tax benefit from stock-based compensation	22	15	2
Proceeds from stock option exercises and other	60	132	8
Net cash provided by (used in) financing activities	396	(497)	(96)
Decrease in cash and cash equivalents	(36)	(127)	(32)
Cash and cash equivalents at beginning of year	187	314	346
Cash and cash equivalents at end of year	$ 151	$ 187	$ 314