Fair Value Measurements - Fair Value & Carrying Value Hierarchy Basis (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Assets
Restricted cash and restricted cash equivalents	$ 487	$ 405	$ 420
Total Fair Value
Assets
Cash and cash equivalents	2,740	1,227
Investment securities	1,862	1,884
Net finance receivables, less allowance for finance receivable losses	17,914	19,319
Restricted cash and restricted cash equivalents	487	405
Other assets	67	84
Liabilities
Long-term debt	18,584	18,509
Total Carrying Value
Assets
Cash and cash equivalents	2,740	1,227
Investment securities	1,862	1,884
Net finance receivables, less allowance for finance receivable losses	15,397	17,560
Restricted cash and restricted cash equivalents	487	405
Other assets	67	74
Liabilities
Long-term debt	18,010	17,212
Level 1
Assets
Cash and cash equivalents	2,740	1,159
Investment securities	39	45
Net finance receivables, less allowance for finance receivable losses	0	0
Restricted cash and restricted cash equivalents	487	405
Other assets	0	0
Liabilities
Long-term debt	0	0
Level 2
Assets
Cash and cash equivalents	0	68
Investment securities	1,819	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	18,584	18,509
Level 3
Assets
Cash and cash equivalents	0	0
Investment securities	4	4
Net finance receivables, less allowance for finance receivable losses	17,914	19,319
Restricted cash and restricted cash equivalents	0	0
Other assets	67	84
Liabilities
Long-term debt	$ 0	$ 0