Retirement Benefits and Trusteed Assets Retirement Benefits and Trusteed Assets (OPEB - Future Payments) (Details) (Other Postretirement Benefit Plan [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2015	$ 77
2016	82
2017	85
2018	89
2019	93
2020 - 2024	505
Total Expected Future Benefit Payments	$ 931