Segment Information Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 41,326	$ 36,451	$ 39,853	$ 39,146	$ 38,654	$ 35,943	$ 37,718	$ 39,485	$ 156,776	$ 151,800	$ 149,558
Long-Lived Assets	63,562				60,901				63,562	60,901	57,256
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									93,844	93,433	93,142
Long-Lived Assets	42,504				42,946				42,504	42,946	39,853
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									9,619	10,041	11,451
Long-Lived Assets	1,691				1,302				1,691	1,302	1,490
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									10,580	10,028	8,978
Long-Lived Assets	4,771				4,264				4,771	4,264	3,814
Germany
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									7,265	7,322	6,950
Long-Lived Assets	3,182				2,254				3,182	2,254	2,203
Other Geographical [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									35,468	30,976	29,037
Long-Lived Assets	$ 11,414				$ 10,135				$ 11,414	$ 10,135	$ 9,896