Fair Value Measurements - Fair Value & Carrying Value Hierarchy Basis (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets
Restricted cash and restricted cash equivalents	$ 451	$ 405	$ 499
Total Fair Value
Assets
Cash and cash equivalents	2,272	1,227
Investment securities	1,922	1,884
Net finance receivables, less allowance for finance receivable losses	18,629	19,319
Restricted cash and restricted cash equivalents	451	405
Other assets	62	84
Liabilities
Long-term debt	19,426	18,509
Total Carrying Value
Assets
Cash and cash equivalents	2,272	1,227
Investment securities	1,922	1,884
Net finance receivables, less allowance for finance receivable losses	15,815	17,560
Restricted cash and restricted cash equivalents	451	405
Other assets	62	74
Liabilities
Long-term debt	17,800	17,212
Level 1
Assets
Cash and cash equivalents	2,255	1,159
Investment securities	44	45
Net finance receivables, less allowance for finance receivable losses	0	0
Restricted cash and restricted cash equivalents	451	405
Other assets	0	0
Liabilities
Long-term debt	0	0
Level 2
Assets
Cash and cash equivalents	17	68
Investment securities	1,870	1,835
Net finance receivables, less allowance for finance receivable losses	0	0
Restricted cash and restricted cash equivalents	0	0
Other assets	2	0
Liabilities
Long-term debt	19,426	18,509
Level 3
Assets
Cash and cash equivalents	0	0
Investment securities	8	4
Net finance receivables, less allowance for finance receivable losses	18,629	19,319
Restricted cash and restricted cash equivalents	0	0
Other assets	60	84
Liabilities
Long-term debt	$ 0	$ 0