Non-U.S. Activities - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 10,207	$ 10,360	$ 10,274
Assets	242,698	245,155
United Kingdom
Segment Reporting Information [Line Items]
Revenues	1,050	938	1,020
Non-U.S.
Segment Reporting Information [Line Items]
Revenues	4,419	4,428	$ 4,644
Assets	$ 79,100	$ 78,100