Segment Information - Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Depreciation and amortization	$ (1,285)	$ (910)	$ (3,858)	$ (2,739)
Total other expense, net	(565)	(348)	(1,609)	(999)
Income before income tax expense	329	139	802	486
Income tax expense	57	47	123	214
NET INCOME	272	92	679	272
Operating segments
Segment Reporting Information [Line Items]
Total reportable segment adjusted EBITDA	2,671	1,648	7,875	5,217
Segment Reconciling Items
Segment Reporting Information [Line Items]
Regulatory revenues	178	189	546	544
Depreciation and amortization	(1,285)	(910)	(3,858)	(2,739)
Other operating expenses	(670)	(440)	(2,152)	(1,537)
Total other expense, net	$ (565)	$ (348)	$ (1,609)	$ (999)