Employee Benefit Plans (Fair Values of the Company's Pension Plan Assets by Asset Category) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Total	$ 2,561	$ 4,627
Equity Securities | U.S. | US Large Cap
Fair values of pension plan assets	240	336
Equity Securities | U.S. | US Small Cap
Fair values of pension plan assets	21	104
Equity Securities | U.S. | Treasury Stock
Fair values of pension plan assets	53	87
Equity Securities | Developed Markets | Developed Markets
Fair values of pension plan assets	477	781
Debt Securities | Cash and cash equivalents
Fair values of pension plan assets	224	51
Debt Securities | Corporate | Developed Markets
Fair values of pension plan assets	42	146
Debt Securities | Corporate | United States and Canada
Fair values of pension plan assets	107	1,141
Debt Securities | Diversified
Fair values of pension plan assets	622	581
Debt Securities | Government | Developed Markets
Fair values of pension plan assets	170	383
Debt Securities | Government | United States and Canada
Fair values of pension plan assets	4	238
Debt Securities | Other Debt Securities
Fair values of pension plan assets	15	180
Real Estate And Other
Fair values of pension plan assets	586	599
Level 1
Total	133	351
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	53	87
Level 1 | Equity Securities | Developed Markets | Developed Markets
Fair values of pension plan assets	80	91
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 and Canada
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 and Canada
Fair values of pension plan assets	0	173
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	1,913	3,641
Level 2 | Equity Securities | U.S. | US Large Cap
Fair values of pension plan assets	240	336
Level 2 | Equity Securities | U.S. | US Small Cap
Fair values of pension plan assets	21	104
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	397	690
Level 2 | Debt Securities | Cash and cash equivalents
Fair values of pension plan assets	224	51
Level 2 | Debt Securities | Corporate | Developed Markets
Fair values of pension plan assets	42	146
Level 2 | Debt Securities | Corporate | United States and Canada
Fair values of pension plan assets	21	1,016
Level 2 | Debt Securities | Diversified
Fair values of pension plan assets	622	581
Level 2 | Debt Securities | Government | Developed Markets
Fair values of pension plan assets	170	383
Level 2 | Debt Securities | Government | United States and Canada
Fair values of pension plan assets	4	65
Level 2 | Debt Securities | Other Debt Securities
Fair values of pension plan assets	0	159
Level 2 | Real Estate And Other
Fair values of pension plan assets	172	110
Level 3
Fair values of pension plan assets	515	635	$ 612
Total	515	635
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 and Canada
Fair values of pension plan assets	86	125
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 and Canada
Fair values of pension plan assets	0	0
Level 3 | Debt Securities | Other Debt Securities
Fair values of pension plan assets	15	21
Level 3 | Real Estate And Other
Fair values of pension plan assets	$ 414	$ 489