Non-U.S. Activities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 3,019	$ 2,668
Assets	250,286		$ 238,425
Non-U.S.
Segment Reporting Information [Line Items]
Revenues	1,321	1,096
Assets	$ 78,500	$ 71,600