Acquisitions, Investments and Dispositions - Pro Forma Supplemental Information (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Dec. 13, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Combinations [Abstract]
Revenues			$ 12,337	$ 12,033	$ 12,075
Net income			1,382	1,525	$ 1,245
If Acquired January 1, 2017 (a)(b)
Revenue			12,655	12,331
Net income			1,279	1,612
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Interest expense			37	38
Business acquisition, pre-tax gain from interests in projects	$ 131			131
Pro Forma
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Income from equity method investment			33	$ 32
Term Loan
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Short-term borrowings		$ 825	$ 825
Fixed interest rate		4.64%	4.64%