Schedule I - Parent Company Financial Information (Condensed Statements of Cash Flows) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 1,618	$ 1,716	$ 1,923
Cash flows from investing activities:
Acquisitions	(18)	(187)	(1,235)
Purchases of investment securities	(2,883)	(3,261)	(3,221)
Proceeds from sale of investment securities	2,409	1,592	1,404
Maturities of investment securities	885	1,077	1,497
Purchases of property and equipment, net	(528)	(441)	(410)
Net cash used in investing activities	(63)	(1,182)	(1,965)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	1,733	0	990
Repayments of Long-term Debt	(500)us-gaap_RepaymentsOfLongTermDebt	0us-gaap_RepaymentsOfLongTermDebt	(36)us-gaap_RepaymentsOfLongTermDebt
Change in book overdraft	(69)	79	18
Common stock repurchases	(872)	(531)	(518)
Dividends paid	(172)us-gaap_PaymentsOfDividends	(168)us-gaap_PaymentsOfDividends	(165)us-gaap_PaymentsOfDividends
Tax benefit from stock-based compensation	12	8	22
Proceeds from stock option exercises and other	29	60	57
Net cash used in financing activities	(758)	(702)	(29)
Increase (decrease) in cash and cash equivalents	797	(168)	(71)
Cash and cash equivalents at beginning of year	1,138	1,306	1,377
Cash and cash equivalents at end of year	1,935	1,138	1,306
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	1,499	1,554	1,611
Cash flows from investing activities:
Acquisitions	0	0	(1,235)
Capital contributions to operating subsidiaries	(442)	(521)	(629)
Purchases of investment securities	(629)	(320)	(338)
Proceeds from sale of investment securities	606	35	127
Maturities of investment securities	149	104	316
Purchases of property and equipment, net	(380)	(223)	(284)
Net cash used in investing activities	(696)	(925)	(2,043)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	1,733	0	990
Repayments of Long-term Debt	(500)	0	0
Change in book overdraft	(5)	7	7
Common stock repurchases	(872)	(531)	(518)
Dividends paid	(172)	(168)	(165)
Tax benefit from stock-based compensation	12	8	22
Proceeds from stock option exercises and other	51	65	60
Net cash used in financing activities	247	(619)	396
Increase (decrease) in cash and cash equivalents	1,050	10	(36)
Cash and cash equivalents at beginning of year	161	151	187
Cash and cash equivalents at end of year	$ 1,211	$ 161	$ 151

Capital contributions to operating subsidiaries

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of cash inflow from realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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The cash outflow to reacquire common stock during the period.

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The cash outflow to acquire debt securities classified as available-for-sale securities, because they are not classified as either held-to-maturity securities or trading securities.

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The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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