Pension and Other Postemployment Benefits (Details Textuals) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 01, 2014
Defined Benefit Plan Disclosure [Line Items]
Mark-to-market adjustment	$ 1,243	$ (396)	$ 875
Mark-to-market adjustment, net of capitalized amounts	835	(256)	609
Decrease in discount rate	(0.75%)
Estimated future employer contributions in next fiscal year	143
Pensions and OPEB
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets	387	(22)
Actual return on plan assets (percent)	6.20%	(0.30%)
Expected return on plan assets	496	535
Pensions
Defined Benefit Plan Disclosure [Line Items]
Decrease in underfunded status				40
Actual return on plan assets	349	(77)
Expected long-term return on plan assets	7.75%	7.75%	7.75%
Expected return on plan assets	462	501	486
Increase in benefit obligation	373
Estimated 2014 amortization of prior service costs (credits) from AOCI	9
Excluded from total investments	92	(87)
OPEB
Defined Benefit Plan Disclosure [Line Items]
Decrease in underfunded status	97
Actual return on plan assets	38	56
Expected long-term return on plan assets	7.75%	7.75%	7.75%
Expected return on plan assets	34	34	37
Increase in benefit obligation	21
Estimated 2014 amortization of prior service costs (credits) from AOCI	(134)
Excluded from total investments	$ (9)	$ (9)