Employee Benefit Plans (Fair Values of the Company's Pension Plan Assets by Asset Category) (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Total	$ 4,627	$ 4,839
Equity Securities | U.S. | US Large Cap
Fair values of pension plan assets	336	278
Equity Securities | U.S. | US Small Cap
Fair values of pension plan assets	104	112
Equity Securities | U.S. | Treasury Stock
Fair values of pension plan assets	87	102
Equity Securities | Developed Markets | Developed Markets
Fair values of pension plan assets	781	795
Debt Securities | Cash and cash equivalents
Fair values of pension plan assets	51	40
Debt Securities | Corporate | Developed Markets
Fair values of pension plan assets	146	232
Debt Securities | Corporate | United States
Fair values of pension plan assets	1,141	1,245
Debt Securities | Diversified
Fair values of pension plan assets	581	477
Debt Securities | Government | Developed Markets
Fair values of pension plan assets	383	504
Debt Securities | Government | United States
Fair values of pension plan assets	238	265
Debt Securities | Other Debt Securities
Fair values of pension plan assets	180	175
Real Estate And Other
Fair values of pension plan assets	599	614
Level 1
Total	351	432
Level 1 | Equity Securities | U.S. | US Large Cap
Fair values of pension plan assets	0	0
Level 1 | Equity Securities | U.S. | US Small Cap
Fair values of pension plan assets	0	0
Level 1 | Equity Securities | U.S. | Treasury Stock
Fair values of pension plan assets	87	102
Level 1 | Equity Securities | Developed Markets | Developed Markets
Fair values of pension plan assets	91	107
Level 1 | Debt Securities | Cash and cash equivalents
Fair values of pension plan assets	0	0
Level 1 | Debt Securities | Corporate | Developed Markets
Fair values of pension plan assets	0	0
Level 1 | Debt Securities | Corporate | United States
Fair values of pension plan assets	0	0
Level 1 | Debt Securities | Diversified
Fair values of pension plan assets	0	0
Level 1 | Debt Securities | Government | Developed Markets
Fair values of pension plan assets	0	0
Level 1 | Debt Securities | Government | United States
Fair values of pension plan assets	173	223
Level 1 | Debt Securities | Other Debt Securities
Fair values of pension plan assets	0	0
Level 1 | Real Estate And Other
Fair values of pension plan assets	0	0
Level 2
Total	3,641	3,795
Level 2 | Equity Securities | U.S. | US Large Cap
Fair values of pension plan assets	336	278
Level 2 | Equity Securities | U.S. | US Small Cap
Fair values of pension plan assets	104	112
Level 2 | Equity Securities | U.S. | Treasury Stock
Fair values of pension plan assets	0	0
Level 2 | Equity Securities | Developed Markets | Developed Markets
Fair values of pension plan assets	690	688
Level 2 | Debt Securities | Cash and cash equivalents
Fair values of pension plan assets	51	40
Level 2 | Debt Securities | Corporate | Developed Markets
Fair values of pension plan assets	146	232
Level 2 | Debt Securities | Corporate | United States
Fair values of pension plan assets	1,016	1,121
Level 2 | Debt Securities | Diversified
Fair values of pension plan assets	581	477
Level 2 | Debt Securities | Government | Developed Markets
Fair values of pension plan assets	383	504
Level 2 | Debt Securities | Government | United States
Fair values of pension plan assets	65	42
Level 2 | Debt Securities | Other Debt Securities
Fair values of pension plan assets	159	153
Level 2 | Real Estate And Other
Fair values of pension plan assets	110	148
Level 3
Fair values of pension plan assets	635	612	$ 632
Total	635	612
Level 3 | Equity Securities | U.S. | US Large Cap
Fair values of pension plan assets	0	0
Level 3 | Equity Securities | U.S. | US Small Cap
Fair values of pension plan assets	0	0
Level 3 | Equity Securities | U.S. | Treasury Stock
Fair values of pension plan assets	0	0
Level 3 | Equity Securities | Developed Markets | Developed Markets
Fair values of pension plan assets	0	0
Level 3 | Debt Securities | Cash and cash equivalents
Fair values of pension plan assets	0	0
Level 3 | Debt Securities | Corporate | Developed Markets
Fair values of pension plan assets	0	0
Level 3 | Debt Securities | Corporate | United States
Fair values of pension plan assets	125	124
Level 3 | Debt Securities | Diversified
Fair values of pension plan assets	0	0
Level 3 | Debt Securities | Government | Developed Markets
Fair values of pension plan assets	0	0
Level 3 | Debt Securities | Government | United States
Fair values of pension plan assets	0	0
Level 3 | Debt Securities | Other Debt Securities
Fair values of pension plan assets	21	22
Level 3 | Real Estate And Other
Fair values of pension plan assets	$ 489	$ 466