Equity in Net Assets of Non-consolidated Affiliates (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Noncontrolling Interest [Line Items]
Finance charge income	$ 999	$ 1,043	$ 2,971	$ 3,038
Income before income taxes	1,207	711	1,663	1,606
Net income	46	39	113	126
Joint Ventures [Member]
Noncontrolling Interest [Line Items]
Finance charge income	355	330	1,049	1,024
Income before income taxes	174	150	428	481
Net income	131	$ 113	321	$ 361
Undistributed earnings	609		$ 609		$ 615
SAIC-GMAC [Member]
Noncontrolling Interest [Line Items]
Cash dividends	294
Proceeds from dividends received	$ 103