Segment Information - Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total reportable segment adjusted EBITDA	$ 767	$ 367	$ 1,517	$ 998
Depreciation and amortization	(1,290)	(949)	(2,573)	(1,829)
Total other expense, net	(530)	(327)	(1,044)	(651)
INCOME BEFORE INCOME TAX EXPENSE	237	40	473	347
Income tax (benefit) expense	55	(23)	(66)	(167)
NET INCOME	292	17	407	180
Operating segments
Segment Reporting Information [Line Items]
Total reportable segment adjusted EBITDA	2,624	1,738	5,204	3,569
Segment Reconciling Items
Segment Reporting Information [Line Items]
Regulatory revenues	185	183	368	355
Depreciation and amortization	(1,290)	(949)	(2,573)	(1,829)
Other operating expenses	(752)	(605)	(1,482)	(1,097)
Total other expense, net	$ (530)	$ (327)	$ (1,044)	$ (651)