Pension Benefits (Narrative) (Details) (Pension Benefits [Member], USD $)
In Millions, unless otherwise specified

12 Months Ended

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2009

Defined Benefit Plan Disclosure [Line Items]

Pension liability

$ 1,439

Increase to regulatory assets

1,402

Debit to OCI

15

Net loss estimated to be amortized

703

Prior service cost estimated to be amortized

8

Investments value

129

119

Accumulated benefit obligation

10,595

9,319

8,598

Assumptions used in calculating net periodic benefit cost

To determine the assumed discount rate, the Companies use a model that produces a yield curve based on yields on selected highly rated (Aaa or Aa, by Moody's Investors Service) corporate bonds. Bonds with insufficient liquidity, bonds with questionable pricing information and bonds that are not representative of the overall market are excluded from consideration. For example, the bonds used in the model cannot be callable, they must have a price between 50 and 200, the yield must lie between 1 percent and 20 percent, and the amount of the issue must be in excess of $100 million. The spot rates defined by the yield curve and the plan's projected benefit payments are used to develop a weighted average discount rate.

Estimated future employer contributions

759

Other Nonqualified Supplemental Defined Benefit Pension [Member]

Defined Benefit Plan Disclosure [Line Items]

Accumulated benefit obligation

$ 208

$ 192