Employee Benefits - Fair Values of Pension Plan Assets by Asset Category (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	$ 942	$ 918
Insurance company contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	12	12
Multi-strategy investment funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	56	4
Equity securities [Member] | U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	216	336
Equity securities [Member] | International equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	29	39
Equity securities [Member] | Emerging markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		1
Fixed income securities [Member] | Corporate bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	73	70
Fixed income securities [Member] | Corporate bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	10	7
Fixed income securities [Member] | Government bonds and agency bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	79	73
Fixed income securities [Member] | Government bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	3	3
Fixed income securities [Member] | State and municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1
Fixed income securities [Member] | Convertible securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		1
Mutual funds [Member] | U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	13	11
Mutual funds [Member] | International equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	8	150
Mutual funds [Member] | Fixed Income - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	4	4
Mutual funds [Member] | Fixed income - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	2	2
Mutual funds [Member] | Government bonds and agency bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		72
Common trust funds [Member] | U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	24	21
Common trust funds [Member] | International equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	147
Common trust funds [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	5	4
Common trust funds [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	48	40
Common trust funds [Member] | Emerging markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	47	24
Common trust funds [Member] | Convertible securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	47	44
Common trust funds [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	118
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	270	614
Level 1 [Member] | Equity securities [Member] | U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	216	336
Level 1 [Member] | Equity securities [Member] | International equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	29	39
Level 1 [Member] | Equity securities [Member] | Emerging markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		1
Level 1 [Member] | Mutual funds [Member] | U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	13	11
Level 1 [Member] | Mutual funds [Member] | International equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	6	149
Level 1 [Member] | Mutual funds [Member] | Fixed Income - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	4	4
Level 1 [Member] | Mutual funds [Member] | Fixed income - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	2	2
Level 1 [Member] | Mutual funds [Member] | Government bonds and agency bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		72
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	604	288
Level 2 [Member] | Fixed income securities [Member] | Corporate bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	73	70
Level 2 [Member] | Fixed income securities [Member] | Corporate bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	10	7
Level 2 [Member] | Fixed income securities [Member] | Government bonds and agency bonds - U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	79	73
Level 2 [Member] | Fixed income securities [Member] | Government bonds - International [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	3	3
Level 2 [Member] | Fixed income securities [Member] | State and municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1
Level 2 [Member] | Fixed income securities [Member] | Convertible securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value		1
Level 2 [Member] | Mutual funds [Member] | International equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	2	1
Level 2 [Member] | Common trust funds [Member] | U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	24	21
Level 2 [Member] | Common trust funds [Member] | International equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	147
Level 2 [Member] | Common trust funds [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	5	4
Level 2 [Member] | Common trust funds [Member] | Short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	48	40
Level 2 [Member] | Common trust funds [Member] | Emerging markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	47	24
Level 2 [Member] | Common trust funds [Member] | Convertible securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	47	44
Level 2 [Member] | Common trust funds [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	118
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	68	16
Level 3 [Member] | Insurance company contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	12	12
Level 3 [Member] | Multi-strategy investment funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	$ 56	$ 4