Retirement Benefits and Trusteed Assets Retirement Benefits and Trusteed Assets (VEBA Trust) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contribution of common stock to VEBA Trust	$ 117
Other Postretirement Benefits
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contribution of common stock to VEBA Trust	117
VEBA Trust [Member] | Other Postretirement Benefits
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contributions to Master VEBA Trust, Number of shares	1,427,835
Price Per Share	$ 81.91
Contribution of common stock to VEBA Trust	$ 117