Employee Benefit Plans (Details 5) (Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair values of other postretirement benefits plan assets
Total assets at fair value	$ 175	$ 159	$ 162
Cash management fund [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	14	16
U.S. large cap [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	42	42
U.S. small cap [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	21	20
International developed markets large cap growth [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	13	13
Emerging markets growth [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	5	2
Preferred stock [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	1
Equities - U.S. large cap [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	15	15
Equities - Emerging markets value [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	3	3
Equities - International developed markets large cap value [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	9	7
Fixed income - Corporate bonds [Member] | Commingled investment funds - fixed income [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	15	6
U.S. Treasury securities [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	2	2
Government and municipal bonds [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	10	10
Mortgage-backed securities [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	7	6
Corporate bonds [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	18	17
Level 1 [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	81	82
Level 1 [Member] | Cash management fund [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	14	16
Level 1 [Member] | U.S. large cap [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	42	42
Level 1 [Member] | U.S. small cap [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	21	20
Level 1 [Member] | International developed markets large cap growth [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	1
Level 1 [Member] | Emerging markets growth [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	1	1
Level 1 [Member] | Preferred stock [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	1
Level 1 [Member] | Equities - U.S. large cap [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 1 [Member] | Equities - Emerging markets value [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 1 [Member] | Equities - International developed markets large cap value [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 1 [Member] | Fixed income - Corporate bonds [Member] | Commingled investment funds - fixed income [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 1 [Member] | U.S. Treasury securities [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	2	2
Level 1 [Member] | Government and municipal bonds [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 1 [Member] | Mortgage-backed securities [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 1 [Member] | Corporate bonds [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 2 [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	94	77
Level 2 [Member] | Cash management fund [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 2 [Member] | U.S. large cap [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 2 [Member] | U.S. small cap [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 2 [Member] | International developed markets large cap growth [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	13	12
Level 2 [Member] | Emerging markets growth [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	4	1
Level 2 [Member] | Preferred stock [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0
Level 2 [Member] | Equities - U.S. large cap [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	15	15
Level 2 [Member] | Equities - Emerging markets value [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	3	3
Level 2 [Member] | Equities - International developed markets large cap value [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	9	7
Level 2 [Member] | Fixed income - Corporate bonds [Member] | Commingled investment funds - fixed income [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	15	6
Level 2 [Member] | U.S. Treasury securities [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 2 [Member] | Government and municipal bonds [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	10	10
Level 2 [Member] | Mortgage-backed securities [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	7	6
Level 2 [Member] | Corporate bonds [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	18	17
Level 3 [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Cash management fund [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | U.S. large cap [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | U.S. small cap [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | International developed markets large cap growth [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Emerging markets growth [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Preferred stock [Member] | Equity securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0
Level 3 [Member] | Equities - U.S. large cap [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Equities - Emerging markets value [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Equities - International developed markets large cap value [Member] | Commingled investment funds - equities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Fixed income - Corporate bonds [Member] | Commingled investment funds - fixed income [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | U.S. Treasury securities [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Government and municipal bonds [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Mortgage-backed securities [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	0	0
Level 3 [Member] | Corporate bonds [Member] | Fixed income securities [Member]
Fair values of other postretirement benefits plan assets
Total assets at fair value	$ 0	$ 0