Fair Value (Fair Value Measurements - Nonrecurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	$ 425	$ 108
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	157	77
Lower of cost or fair value or valuation reserve allowance	0	0
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	64	20
Lower of cost or fair value or valuation reserve allowance	(10)	(3)
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	33	22
Lower of cost or fair value or valuation reserve allowance	(25)	(12)
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	97	42
Lower of cost or fair value or valuation reserve allowance	(35)	(15)
Fair Value, measurements, nonrecurring | Nonmarketable equity investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value	1
Lower of cost or fair value or valuation reserve allowance	0
Fair Value, measurements, nonrecurring | Repossessed and foreclosed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value	13	14
Lower of cost or fair value or valuation reserve allowance	(1)	(1)
Fair Value, measurements, nonrecurring | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value		3
Lower of cost or fair value or valuation reserve allowance		0
Fair Value, measurements, nonrecurring | Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	268	136
Lower of cost or fair value or valuation reserve allowance	(36)	(16)
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 | Nonmarketable equity investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value	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, repossessed and foreclosed, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 1 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value		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 | 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 | Nonmarketable equity investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value	1
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, repossessed and foreclosed, fair value	0	0
Fair Value, measurements, nonrecurring | Fair value, inputs, level 2 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value		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	1	0
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	157	77
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	64	20
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	33	22
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	97	42
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Nonmarketable equity investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value	0
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, repossessed and foreclosed, fair value	13	14
Fair Value, measurements, nonrecurring | Fair value, inputs, level 3 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, repossessed and foreclosed, fair value		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	$ 267	$ 136