Employee Benefit Plan - Fair Value of Plan Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	$ 217	$ 190
Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	61	55
Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	6	5
Equity Index Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	75	67
Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	1
Bond Index Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	74	63
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	62	55
Level 1 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	61	55
Level 1 [Member] | Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 1 [Member] | Equity Index Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 1 [Member] | Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	1
Level 1 [Member] | Bond Index Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	155	135
Level 2 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 2 [Member] | Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	6	5
Level 2 [Member] | Equity Index Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	75	67
Level 2 [Member] | Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 2 [Member] | Bond Index Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis	74	63
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 3 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 3 [Member] | Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 3 [Member] | Equity Index Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 3 [Member] | Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis
Level 3 [Member] | Bond Index Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets measured at fair value on a recurring basis