Segment Information - Schedule of Revenue by Geographical Area (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	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers [Line Items]
Revenues	$ 5,949	$ 6,512	$ 7,141	$ 6,505	$ 7,320	$ 7,500	$ 7,776	$ 7,794	$ 26,107	$ 30,390	$ 32,639
United States [Member]
Revenues from External Customers [Line Items]
Revenues									18,194	19,354	21,234
Europe [Member]
Revenues from External Customers [Line Items]
Revenues									5,311	6,365	7,528
Other Countries [Member]
Revenues from External Customers [Line Items]
Revenues									$ 2,602	$ 4,671	$ 3,877