Retirement Benefits (Unaudited) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended		3 Months Ended				1 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2013 Pension Employer Required Minimum Contribution	Dec. 31, 2013 OPEB Employer Required Minimum Contribution	Mar. 31, 2013 Pension Benefits	Mar. 31, 2012 Pension Benefits	Mar. 31, 2013 Medical and Life Benefits	Mar. 31, 2012 Medical and Life Benefits	Apr. 24, 2013 Defined Benefit Pension Plan Employer Contribution, Voluntary
Components of Net Periodic Benefit Cost
Service cost					$ 129	$ 131	$ 9	$ 8
Interest cost					279	296	24	27
Expected return on plan assets					(453)	(427)	(19)	(17)
Amortization of:
Prior service cost (credit)					(14)	(15)	(12)	(12)
Net loss from previous years					152	107	7	5
Other					0	2	0	0
Net periodic benefit cost					93	94	9	11
Employer Contributions
Expected contributions in current fiscal year			66	110
Employer contributions	(26)	(17)			26		8		500
Defined contribution plan contributions	$ 75	$ 76