Plan Assets Using Fair Value Hierarchy (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	$ 1,134	$ 1,078
U.S. Equity | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	111	122
U.S. Equity | Overlay derivatives liabilities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	(5)	(8)
Global ex U.S. Equity
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	109
Global ex U.S. Equity | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets		93
Global ex U.S. Equity | Overlay derivatives liabilities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets		(6)
Global ex Emerging Markets Equity
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	53	41
Emerging Markets Equity | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	28	43
Emerging Markets Equity | Overlay derivatives liabilities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets		(3)
Emerging Markets Equity | Overlay derivatives assets
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	17
Absolute Return Hedge Funds
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	188	150
Equity Hedge Funds
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	155	123
Private Equity
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	51	51
Private Real Assets
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	33	24
Public Real Assets
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	22	23
Fixed Income | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	346	375
Fixed Income | Overlay derivatives liabilities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	(12)	27
Cash Equivalents
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	38	23
Level 1
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	15	290
Level 1 | U.S. Equity | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	15	49
Level 1 | Fixed Income | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets		241
Level 2
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	644	379
Level 2 | U.S. Equity | Overlay derivatives liabilities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	(5)	(8)
Level 2 | Global ex U.S. Equity
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	109
Level 2 | Global ex U.S. Equity | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets		93
Level 2 | Global ex U.S. Equity | Overlay derivatives liabilities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets		(6)
Level 2 | Global ex Emerging Markets Equity
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	31	25
Level 2 | Emerging Markets Equity | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	28	43
Level 2 | Emerging Markets Equity | Overlay derivatives liabilities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets		(3)
Level 2 | Emerging Markets Equity | Overlay derivatives assets
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	17
Level 2 | Absolute Return Hedge Funds
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	58	40
Level 2 | Equity Hedge Funds
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	74	62
Level 2 | Public Real Assets
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	22	14
Level 2 | Fixed Income | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	284	69
Level 2 | Fixed Income | Overlay derivatives liabilities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	(12)	27
Level 2 | Cash Equivalents
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	38	23
Level 3
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	475	409
Level 3 | U.S. Equity | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	96	73
Level 3 | Global ex Emerging Markets Equity
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	22	16
Level 3 | Absolute Return Hedge Funds
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	130	110
Level 3 | Equity Hedge Funds
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	81	61
Level 3 | Private Equity
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	51	51
Level 3 | Private Real Assets
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	33	24
Level 3 | Public Real Assets
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets		9
Level 3 | Fixed Income | Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Fair value of plan assets	$ 62	$ 65