Segment Information (Details) - Enterprise-Wide Disclosures - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues based on location
Benchmark percentage of revenue transactions from a single customer									10.00%	10.00%	10.00%
Total revenues	$ 7,796	$ 7,723	$ 7,477	$ 7,286	$ 7,451	$ 7,325	$ 7,184	$ 6,942	$ 30,282	$ 28,902	$ 27,625
United States [Member]
Revenues based on location
Total revenues									28,418	27,253	25,904
Non-U.S. [Member]
Revenues based on location
Total revenues									1,864	1,649	1,721
Canada
Revenues based on location
Total revenues									1,293	1,232	1,154
Other Non-U.S. [Member]
Revenues based on location
Total revenues									$ 571	$ 417	$ 567