Fair Value Measurements - Fair Value & Carrying Value Hierarchy Basis (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Assets
Restricted cash and restricted cash equivalents	$ 497	$ 405	$ 434
Total Fair Value
Assets
Cash and cash equivalents	1,944	1,227
Investment securities	1,882	1,884
Net finance receivables, less allowance for finance receivable losses	18,176	19,319
Restricted cash and restricted cash equivalents	497	405
Other assets	62	84
Liabilities
Long-term debt	18,702	18,509
Total Carrying Value
Assets
Cash and cash equivalents	1,944	1,227
Investment securities	1,882	1,884
Net finance receivables, less allowance for finance receivable losses	15,493	17,560
Restricted cash and restricted cash equivalents	497	405
Other assets	62	74
Liabilities
Long-term debt	17,531	17,212
Level 1
Assets
Cash and cash equivalents	1,944	1,159
Investment securities	42	45
Net finance receivables, less allowance for finance receivable losses	0	0
Restricted cash and restricted cash equivalents	497	405
Other assets	0	0
Liabilities
Long-term debt	0	0
Level 2
Assets
Cash and cash equivalents	0	68
Investment securities	1,833	1,835
Net finance receivables, less allowance for finance receivable losses	0	0
Restricted cash and restricted cash equivalents	0	0
Other assets	0	0
Liabilities
Long-term debt	18,702	18,509
Level 3
Assets
Cash and cash equivalents	0	0
Investment securities	7	4
Net finance receivables, less allowance for finance receivable losses	18,176	19,319
Restricted cash and restricted cash equivalents	0	0
Other assets	62	84
Liabilities
Long-term debt	$ 0	$ 0