Fair Value (Fair Value Measurements - Nonrecurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	$ 441	$ 158
Finance receivables and loans, net	114,649	126,968
Loans held-for-sale | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	285	128
Lower of cost or fair value, valuation reserve, or cumulative adjustments	0	0
Nonmarketable equity investments | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	26	12
Lower of cost or fair value, valuation reserve, or cumulative adjustments	15	0
Equity Method Investments | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure		4
Lower of cost or fair value, valuation reserve, or cumulative adjustments		(6)
Repossessed And Foreclosed Assets Member | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	6	12
Lower of cost or fair value, valuation reserve, or cumulative adjustments	(1)	(1)
Assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	389	265
Lower of cost or fair value, valuation reserve, or cumulative adjustments	(10)	(40)
Fair value, inputs, level 1 | Loans held-for-sale | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0
Fair value, inputs, level 1 | Nonmarketable equity investments | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	0
Fair value, inputs, level 1 | Equity Method Investments | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure		0
Fair value, inputs, level 1 | Repossessed And Foreclosed Assets Member | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	0
Fair value, inputs, level 1 | Assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	0	0
Fair value, inputs, level 2 | Loans held-for-sale | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0
Fair value, inputs, level 2 | Nonmarketable equity investments | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	21	5
Fair value, inputs, level 2 | Equity Method Investments | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure		0
Fair value, inputs, level 2 | Repossessed And Foreclosed Assets Member | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	0
Fair value, inputs, level 2 | Assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	21	5
Fair value, inputs, level 3 | Loans held-for-sale | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	285	128
Fair value, inputs, level 3 | Nonmarketable equity investments | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	5	7
Fair value, inputs, level 3 | Equity Method Investments | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure		4
Fair value, inputs, level 3 | Repossessed And Foreclosed Assets Member | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	6	12
Fair value, inputs, level 3 | Assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	368	260
Commercial portfolio segment | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	72	109
Lower of cost or fair value, valuation reserve, or cumulative adjustments	(24)	(33)
Commercial portfolio segment | Fair value, inputs, level 1 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0
Commercial portfolio segment | Fair value, inputs, level 2 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0
Commercial portfolio segment | Fair value, inputs, level 3 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	72	109
Automotive loan | Commercial portfolio segment | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	13	64
Lower of cost or fair value, valuation reserve, or cumulative adjustments	(11)	(12)
Automotive loan | Commercial portfolio segment | Fair value, inputs, level 1 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0
Automotive loan | Commercial portfolio segment | Fair value, inputs, level 2 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0
Automotive loan | Commercial portfolio segment | Fair value, inputs, level 3 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	13	64
Other loan | Commercial portfolio segment | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	59	45
Lower of cost or fair value, valuation reserve, or cumulative adjustments	(13)	(21)
Other loan | Commercial portfolio segment | Fair value, inputs, level 1 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0
Other loan | Commercial portfolio segment | Fair value, inputs, level 2 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0
Other loan | Commercial portfolio segment | Fair value, inputs, level 3 | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	$ 59	$ 45