Segment Information Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 39,715	$ 36,990	$ 38,853	$ 40,342	$ 41,793	$ 37,666	$ 38,920	$ 41,959	$ 155,900	$ 160,338	$ 156,776
Long-Lived Assets	65,699				65,297				65,699	65,297	63,562
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									98,729	97,546	93,844
Long-Lived Assets	46,434				44,940				46,434	44,940	42,504
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									10,855	10,541	10,580
Long-Lived Assets	4,842				4,604				4,842	4,604	4,771
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									8,899	9,703	9,619
Long-Lived Assets	1,541				1,650				1,541	1,650	1,691
Germany
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									7,930	7,894	7,265
Long-Lived Assets	3,225				3,593				3,225	3,593	3,182
Other Geographical
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									29,487	34,654	35,468
Long-Lived Assets	$ 9,657				$ 10,510				$ 9,657	$ 10,510	$ 11,414