Segment Information - Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total reportable segment adjusted EBITDA	$ 750	$ 631
Depreciation and amortization	(1,283)	(880)
Total other expense, net	(514)	(324)
INCOME BEFORE INCOME TAX EXPENSE	236	307
Income tax expense	(121)	(144)
NET INCOME	115	163
Operating segments
Segment Reporting Information [Line Items]
Total reportable segment adjusted EBITDA	2,536	1,831
Segment Reconciling Items
Segment Reporting Information [Line Items]
Regulatory revenues	183	172
Depreciation and amortization	(1,283)	(880)
Other operating expenses	(686)	(492)
Total other expense, net	$ (514)	$ (324)