Pension and Other Postretirement Benefits - Schedule of Fair Value of Plan Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 1,397	$ 1,557
Pension Benefits [Member] | Equity Securities Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	311	341
Pension Benefits [Member] | Equity Securities International [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	216	255
Pension Benefits [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	820	916
Pension Benefits [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	50	45
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	326	340
Other Postretirement Benefits [Member] | Equity Securities Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	197	208
Other Postretirement Benefits [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	120	126
Other Postretirement Benefits [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	9	6
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	385	427
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Pension Benefits [Member] | Equity Securities Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	120	128
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Pension Benefits [Member] | Equity Securities International [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	215	254
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Pension Benefits [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	50	45
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	326	340
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Other Postretirement Benefits [Member] | Equity Securities Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	197	208
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Other Postretirement Benefits [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	120	126
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Other Postretirement Benefits [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	9	6
Significant Other Observable Inputs (Level 2) [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,001	1,118
Significant Other Observable Inputs (Level 2) [Member] | Pension Benefits [Member] | Equity Securities Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	191	213
Significant Other Observable Inputs (Level 2) [Member] | Pension Benefits [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	810	905
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	11	12	$ 12
Significant Unobservable Inputs (Level 3) [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	10	11	11
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1	1	1
Significant Unobservable Inputs (Level 3) [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	11	12
Significant Unobservable Inputs (Level 3) [Member] | Pension Benefits [Member] | Equity Securities International [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1	1
Significant Unobservable Inputs (Level 3) [Member] | Pension Benefits [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	10	11
Investments Measured at Fair Value [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2,018	2,236	2,116
Investments Measured at Fair Value [Member] | Pension Benefits [Member] | Equity Securities Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	33	35
Investments Measured at Fair Value [Member] | Pension Benefits [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	504	543
Investments Measured at Fair Value [Member] | Pension Benefits [Member] | Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	38	47
Investments Measured at Fair Value [Member] | Pension Benefits [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	46	54
Investments Measured at Fair Value [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	348	367	$ 368
Investments Measured at Fair Value [Member] | Other Postretirement Benefits [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 22	$ 27