Employee Benefits (Details 6) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair values of postretirement plan assets by asset category
Assets at fair value	$ 57	$ 61	$ 58
Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	57	61
U.S. equities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	36	45
International equities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	8	9
Convertible securities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	4	4
Short-term investments [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	8	2
Fixed income [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	1	1
Level 1 [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 1 [Member] | U.S. equities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 1 [Member] | International equities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 1 [Member] | Convertible securities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 1 [Member] | Short-term investments [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 1 [Member] | Fixed income [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 2 [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	57	61
Level 2 [Member] | U.S. equities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	36	45
Level 2 [Member] | International equities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	8	9
Level 2 [Member] | Convertible securities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	4	4
Level 2 [Member] | Short-term investments [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	8	2
Level 2 [Member] | Fixed income [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	1	1
Level 3 [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 3 [Member] | U.S. equities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 3 [Member] | International equities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 3 [Member] | Convertible securities [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 3 [Member] | Short-term investments [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	0	0
Level 3 [Member] | Fixed income [Member] | Common Trust Funds [Member]
Fair values of postretirement plan assets by asset category
Assets at fair value	$ 0	$ 0