Non-U.S. Activities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 2,951	$ 2,846	$ 8,996	$ 8,324
Assets	234,007		234,007		$ 238,425
Non-U.S.
Segment Reporting Information [Line Items]
Revenues	1,286	1,219	3,929	3,494
Assets	$ 83,100	$ 81,500	$ 83,100	$ 81,500