Reserves for Losses (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable Reserve Roll Forward [line Items]
Balance, January 1	$ 573	$ 521	$ 467
Provisions	963	937	795
Other	(17)	(26)	(5)
Balance, December 31	619	573	521
Principal Write-Offs [Member]
Accounts Receivable Reserve Roll Forward [line Items]
Net write-offs	$ (900)	$ (859)	$ (736)