Fair Value Measurements (Postretirement Health Care Plan) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Level 1
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	$ 20	$ 38
Level 1 | Common stock and equivalents
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	20	38
Level 1 | Commingled equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Government, agency and government-sponsored enterprise obligations
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Other government bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Corporate bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Commingled bond funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 1 | Commingled short-term investment funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 2
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	143	123
Level 2 | Common stock and equivalents
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	0
Level 2 | Commingled equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	13	55
Level 2 | Government, agency and government-sponsored enterprise obligations
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	11	6
Level 2 | Other government bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	2	1
Level 2 | Corporate bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	18	9
Level 2 | Commingled bond funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	49
Level 2 | Commingled short-term investment funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	99	3
Total
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	163	161
Total | Common stock and equivalents
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	20	38
Total | Commingled equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	13	55
Total | Government, agency and government-sponsored enterprise obligations
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	11	6
Total | Other government bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	2	1
Total | Corporate bonds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	18	9
Total | Commingled bond funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	0	49
Total | Commingled short-term investment funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value plan assets	$ 99	$ 3