Non-U.S. Activities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 3,026	$ 2,810	$ 6,045	$ 5,478
Assets	248,308		248,308		$ 238,425
Non-U.S.
Segment Reporting Information [Line Items]
Revenues	1,322	1,172	2,643	2,268
Assets	$ 84,900	$ 73,200	$ 84,900	$ 73,200