Fair Value Measurements (Narrative) (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments in money market mutual funds classified as cash and cash equivalents	$ 437,000,000
Long-term debt, Fair Value	1,600,000,000
Long-term debt, Face Value	1,492,000,000	2,633,000,000
Common Stock And Equivalents [Member] | Regular Plan [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Securities lending arrangement	173,000,000	92,000,000
Common Stock And Equivalents [Member] | Postretirement Health Care Plan [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Securities lending arrangement	6,000,000	4,000,000
U.S. Government And Agency Obligations [Member] | Regular Plan [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Securities lending arrangement	182,000,000	41,000,000
U.S. Government And Agency Obligations [Member] | Postretirement Health Care Plan [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Securities lending arrangement	6,000,000	2,000,000
Corporate Bonds [Member] | Regular Plan [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Securities lending arrangement	39,000,000	34,000,000
Corporate Bonds [Member] | Postretirement Health Care Plan [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Securities lending arrangement	$ 1,000,000	$ 1,000,000