Retirement Benefits and Trusteed Assets (OPEB - Assumptions used in Determining the PBO and Net Pension Costs) (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Ultimate health care trend rate					4.50%
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.30%	4.95%	4.50%	4.10%	4.95%	4.15%
Health care trend rate pre- and post- 65			6.25%	7.50%	7.50%
Health care trend post 65			6.75%	6.50%	6.50%
Ultimate health care trend rate			4.50%	4.50%
Discount rate (prior to interim remeasurement)	4.15%	4.30%	4.10%	4.95%
Expected long-term rate of return on plan assets			8.00%	8.00%	8.25%
Health care trend rate pre-65			7.50%	7.50%
Health care trend post 65			6.50%	6.50%
Health care trend rate pre- and post- 65					7.00%
Other Postretirement Benefit Plan | Other postretirement benefit costs
Defined Benefit Plan Disclosure [Line Items]
Ultimate health care trend rate			4.50%	4.50%	5.00%