Fair Value (Fair Value Measurements - Nonrecurring Basis) (Details) $ in Millions	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	$ 275	$ 314
Automotive | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		210
Lower of cost or fair value or valuation reserve allowance		(2)
Automotive | Valuation technique, market approach | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		104
Automotive | Valuation technique, discounted cash flow | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		$ 106
Automotive | Minimum | Valuation technique, discounted cash flow | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, measurement input		0.0008
Automotive | Maximum | Valuation technique, discounted cash flow | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, measurement input		0.0109
Automotive | Weighted average | Valuation technique, discounted cash flow | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, measurement input		0.0072
Loans held-for-sale, other | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		$ 96
Lower of cost or fair value or valuation reserve allowance		0
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	253	306
Lower of cost or fair value or valuation reserve allowance	0	(2)
Commercial finance receivables and loans, automotive | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	54	84
Lower of cost or fair value or valuation reserve allowance	(19)	(10)
Commercial finance receivables and loans, other | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	17	55
Lower of cost or fair value or valuation reserve allowance	(30)	(46)
Commercial | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	71	139
Lower of cost or fair value or valuation reserve allowance	(49)	(56)
Repossessed and foreclosed assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	13	13
Lower of cost or fair value or valuation reserve allowance	(1)	(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	9	1
Lower of cost or fair value or valuation reserve allowance	(1)	(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	3	3
Lower of cost or fair value or valuation reserve allowance	(4)	0
Assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	349	462
Lower of cost or fair value or valuation reserve allowance	(55)	(60)
Fair value, inputs, level 1 | Automotive | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		0
Fair value, inputs, level 1 | Loans held-for-sale, other | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		0
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 | Commercial finance receivables and loans, automotive | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	0	0
Fair value, inputs, level 1 | Commercial finance receivables and loans, other | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	0	0
Fair value, inputs, level 1 | Commercial | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	0	0
Fair value, inputs, level 1 | Repossessed and foreclosed assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	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	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	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 | Automotive | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		0
Fair value, inputs, level 2 | Loans held-for-sale, other | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		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 | Commercial finance receivables and loans, automotive | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	0	0
Fair value, inputs, level 2 | Commercial finance receivables and loans, other | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	0	0
Fair value, inputs, level 2 | Commercial | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	0	0
Fair value, inputs, level 2 | Repossessed and foreclosed assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	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	0	0
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	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	0	0
Fair value, inputs, level 3 | Automotive | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		210
Fair value, inputs, level 3 | Loans held-for-sale, other | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		96
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	253	306
Fair value, inputs, level 3 | Commercial finance receivables and loans, automotive | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	54	84
Fair value, inputs, level 3 | Commercial finance receivables and loans, other | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	17	55
Fair value, inputs, level 3 | Commercial | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	71	139
Fair value, inputs, level 3 | Repossessed and foreclosed assets | Fair Value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	13	13
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	9	1
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	3	3
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	$ 349	$ 462