Retirement Plans - Fair Value of Plan's Financial Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	$ 2,251	$ 2,145
Cash and Short-term Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	53	75
U.S. Equities (domestic) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	719	729
International Equities (non-U.S.) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	249	252
Global Equities (domestic and non-U.S.) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	228	216
Treasury and Government Issued [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	222	170
Government Related [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	8	9
Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	148	110
Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	140	127
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	302	291
Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	105	89
Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	60	57
Diversified Commodities Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	17	20
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	822	833
Level 1 [Member] | Cash and Short-term Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	6	3
Level 1 [Member] | U.S. Equities (domestic) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	719	729
Level 1 [Member] | International Equities (non-U.S.) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	72	81
Level 1 [Member] | Global Equities (domestic and non-U.S.) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	10	8
Level 1 [Member] | Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	3	2
Level 1 [Member] | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	12	10
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	972	882
Level 2 [Member] | Cash and Short-term Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	47	72
Level 2 [Member] | International Equities (non-U.S.) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	177	171
Level 2 [Member] | Global Equities (domestic and non-U.S.) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	218	208
Level 2 [Member] | Treasury and Government Issued [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	222	169
Level 2 [Member] | Government Related [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	7	9
Level 2 [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	147	109
Level 2 [Member] | Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	137	124
Level 2 [Member] | Diversified Commodities Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	17	20
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	457	430	377
Level 3 [Member] | Treasury and Government Issued [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets		1
Level 3 [Member] | Government Related [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	1
Level 3 [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	1	1
Level 3 [Member] | Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets		1
Level 3 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	302	291	255
Level 3 [Member] | Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	105	89	75
Level 3 [Member] | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of the plan's financial assets	$ 48	$ 47	$ 45