Pension and Other Postemployment Benefits (Details Textuals) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Feb. 16, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 01, 2014
Defined Benefit Plan Disclosure [Line Items]
Mark-to-market adjustment			$ 369	$ 1,243	$ (396)
Mark-to-market adjustment, net of capitalized amounts			242	835	(256)
Company contributions			143
Estimated 2016 contributions			$ 381
Expected long-term return on plan assets		7.50%
Decrease in mortality rate (percent)			0.25%
Pensions and OPEB
Defined Benefit Plan Disclosure [Line Items]
Actual return (losses) on plan assets			$ (172)	$ 387	$ (22)
Actual return on plan assets (percent)			(2.70%)	6.20%	(0.30%)
Expected return on plan assets			$ 476	$ 496	$ 535
Pensions
Defined Benefit Plan Disclosure [Line Items]
Decrease in underfunded status						$ 40
Company contributions			161	15
Actual return (losses) on plan assets			$ (178)	$ 349
Expected long-term return on plan assets			7.75%	7.75%	7.75%
Expected return on plan assets			$ 443	$ 462	$ 501
Increase in benefit obligation due to RP2014 mortality table			49
Estimated amortization of prior service costs (credits) from AOCI in next fiscal year			8
Excluded from total investments			(7)	92
OPEB
Defined Benefit Plan Disclosure [Line Items]
Effect of plan amendment on accumulated benefit obligation			10	97
Company contributions			17	17
Actual return (losses) on plan assets			$ 6	$ 38
Expected long-term return on plan assets			7.75%	7.75%	7.75%
Expected return on plan assets			$ 33	$ 34	$ 34
Increase in benefit obligation due to RP2014 mortality table			1
Estimated amortization of prior service costs (credits) from AOCI in next fiscal year			(80)
Excluded from total investments			$ (7)	$ (9)
Subsequent Event
Defined Benefit Plan Disclosure [Line Items]
Company contributions	$ 160