Fair Value (Fair Value Measurements - Nonrecurring Basis) (Details) $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	$ 107	$ 314
Fair Value, measurements, nonrecurring | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	18	210
Lower of cost or fair value or valuation reserve allowance	0	(2)
Fair Value, measurements, nonrecurring | Loans held-for-sale, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	74	96
Lower of cost or fair value or valuation reserve allowance	0	0
Fair Value, measurements, nonrecurring | Loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	92	306
Lower of cost or fair value or valuation reserve allowance	0	(2)
Fair Value, measurements, nonrecurring | Commercial finance receivables and loans, automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	83	84
Lower of cost or fair value or valuation reserve allowance	(18)	(10)
Fair Value, measurements, nonrecurring | Commercial finance receivables and loans, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	30	55
Lower of cost or fair value or valuation reserve allowance	(40)	(46)
Fair Value, measurements, nonrecurring | Commercial loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	113	139
Lower of cost or fair value or valuation reserve allowance	(58)	(56)
Fair Value, measurements, nonrecurring | Repossessed and foreclosed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	12	13
Lower of cost or fair value or valuation reserve allowance	(1)	(1)
Fair Value, measurements, nonrecurring | Nonmarketable equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	2	1
Lower of cost or fair value or valuation reserve allowance	0	(1)
Fair Value, measurements, nonrecurring | Equity method investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	1	3
Lower of cost or fair value or valuation reserve allowance	(3)	0
Fair Value, measurements, nonrecurring | Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	220	462
Lower of cost or fair value or valuation reserve allowance	(62)	(60)
Fair Value, measurements, nonrecurring | Fair value, inputs, level 1 | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 1 | Loans held-for-sale, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 1 | Loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 1 | Commercial finance receivables and loans, automotive
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, measurements, nonrecurring | Fair value, inputs, level 1 | Commercial finance receivables and loans, other
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, measurements, nonrecurring | Fair value, inputs, level 1 | Commercial loan
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, measurements, nonrecurring | Fair value, inputs, level 1 | Repossessed and foreclosed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 1 | Nonmarketable equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 1 | Equity method investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 1 | Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 2 | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 2 | Loans held-for-sale, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 2 | Loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 2 | Commercial finance receivables and loans, automotive
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, measurements, nonrecurring | Fair value, inputs, level 2 | Commercial finance receivables and loans, other
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, measurements, nonrecurring | Fair value, inputs, level 2 | Commercial loan
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, measurements, nonrecurring | Fair value, inputs, level 2 | Repossessed and foreclosed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 2 | Nonmarketable equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 2 | Equity method investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 2 | Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	18	210
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Loans held-for-sale, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	74	96
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	92	306
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Commercial finance receivables and loans, automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	83	84
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Commercial finance receivables and loans, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	30	55
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Commercial loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial finance receivables and loans, net, fair value	113	139
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Repossessed and foreclosed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	12	13
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Nonmarketable equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	2	1
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Equity method investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value	1	3
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	$ 220	462
Valuation technique, market approach | Fair Value, measurements, nonrecurring | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		104
Valuation technique, discounted cash flow | Fair Value, measurements, nonrecurring | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net		$ 106
Minimum | Valuation technique, discounted cash flow | Fair Value, measurements, nonrecurring | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, measurement input		0.0008
Maximum | Valuation technique, discounted cash flow | Fair Value, measurements, nonrecurring | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, measurement input		0.0109
Weighted average | Valuation technique, discounted cash flow | Fair Value, measurements, nonrecurring | Automotive
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, measurement input		0.0072