Operating Segments - Geographic Data (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Geographic Data
Revenues	$ 8,786	$ 8,792	$ 8,080	$ 8,398	$ 7,605	$ 5,873	$ 6,078	$ 6,667	$ 34,055	$ 26,223	$ 20,182
Long-lived assets	21,948				21,346				21,948	21,346
United States
Geographic Data
Revenues									28,362	21,443	15,599
Long-lived assets	18,044				17,167				18,044	17,167
Canada
Geographic Data
Revenues									5,693	4,780	$ 4,583
Long-lived assets	$ 3,904				$ 4,179				$ 3,904	$ 4,179