Benefits - Fair Value of Plan Assets (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Pension Plans, Defined Benefit [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	$ 155		$ 133
Pension Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	17		12
Pension Plans, Defined Benefit [Member] | Mutual Fund [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	127	[1]	111	[1]
Pension Plans, Defined Benefit [Member] | Hedge Funds, Multi-strategy [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	11	[2]	10	[2]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	17		12
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	17		12
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual Fund [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0	[1]	0	[1]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Hedge Funds, Multi-strategy [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0	[2]	0	[2]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	138		121
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Mutual Fund [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	127	[1]	111	[1]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Hedge Funds, Multi-strategy [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	11	[2]	10	[2]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Mutual Fund [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0	[1]	0	[1]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Hedge Funds, Multi-strategy [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0	[2]	0	[2]
Other Postretirement Benefit Plans, Defined Benefit [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	129		110
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	3		2
Other Postretirement Benefit Plans, Defined Benefit [Member] | Mutual Fund [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	126	[3]	108	[3]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	129		110
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	3		2
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual Fund [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	126	[3]	108	[3]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Mutual Fund [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0	[3]	0	[3]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Mutual Fund [Member]
Fair Value of Plan Assets [Line Items]
Fair Value of Plan Assets	$ 0	[3]	$ 0	[3]

[1] 1) This commingled fund invests primarily in a diversified portfolio of equity and fixed income funds. As of December 31, 2012, the fund was primarily comprised of approximately 34% large-cap U.S. equities, 7% small-cap U.S. equities, 22% international equities, 28% fixed income securities, and 9% in other investments. As of December 31, 2011, the fund was primarily comprised of approximately 36% large-cap U.S. equities, 6% small-cap U.S. equities, 20% international equities, 30% fixed income securities, and 8% in other investments. These investments are generally redeemable on a daily basis at the net asset value per share of the investment.

[2] 2) Primarily includes hedge funds that invest in multiple strategies, including relative value, opportunistic/macro, long/short equities, merger arbitrage/event driven, credit, and short selling strategies, to generate long-term capital appreciation through a portfolio having a diversified risk profile with relatively low volatility and a low correlation with traditional equity and fixed-income markets. These investments can generally be redeemed effective as of the last day of a calendar quarter at the net asset value per share of the investment with approximately 65 days prior written notice.

[3] 1) This fund of funds primarily invests in a combination of equity, fixed income and short-term mutual funds. As of December 31, 2012, the fund was primarily comprised of approximately 17% large-cap U.S. equities, 3% small-cap U.S. equities, 10% international equities, 53% fixed income securities, 10% cash, and 7% in other investments. As of December 31, 2011, the fund was primarily comprised of approximately 19% large-cap U.S. equities, 2% small-cap U.S. equities, 10% international equities, 55% fixed income securities, 8% cash, and 6% in other investments.