Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses	$ 1,276	$ 1,144
Allowance for Loan and Lease Losses, Write-offs	(377)	(350)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	118	97
Allowance for Loan and Lease Losses Write-offs, Net	(259)	(253)
Provision for Loan Losses Expensed	261	271
Allowance for Loan and Lease Losses, Adjustments, Other		7
Financing Receivable, Allowance for Credit Losses	1,278	1,155
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	88	89
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,190	1,066
Loans and Leases Receivable, Gross	125,327	119,002	$ 122,893
Financing Receivable, Individually Evaluated for Impairment	840	757
Financing Receivable, Collectively Evaluated for Impairment	124,487	118,245
Consumer Portfolio Segment [Member] \| Automobile Loan [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses	1,066	932
Allowance for Loan and Lease Losses, Write-offs	(365)	(341)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	112	90
Allowance for Loan and Lease Losses Write-offs, Net	(253)	(251)
Provision for Loan Losses Expensed	253	267
Allowance for Loan and Lease Losses, Adjustments, Other		7
Financing Receivable, Allowance for Credit Losses	1,066	941
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	40	32
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,026	909
Loans and Leases Receivable, Gross	69,318	65,663	68,071
Financing Receivable, Individually Evaluated for Impairment	463	388
Financing Receivable, Collectively Evaluated for Impairment	68,855	65,275
Consumer Portfolio Segment [Member] \| Residential Mortgage [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses	79	91
Allowance for Loan and Lease Losses, Write-offs	(12)	(9)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	6	7
Allowance for Loan and Lease Losses Write-offs, Net	(6)	(2)
Provision for Loan Losses Expensed	1	(3)
Allowance for Loan and Lease Losses, Adjustments, Other		0
Financing Receivable, Allowance for Credit Losses	74	86
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	27	33
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	47	53
Loans and Leases Receivable, Gross	14,683	10,937	13,750
Financing Receivable, Individually Evaluated for Impairment	230	249
Financing Receivable, Collectively Evaluated for Impairment	14,453	10,688
Commercial Portfolio Segment [Member] \| Commercial Loan [Member]
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Financing Receivable, Allowance for Credit Losses	131	121
Allowance for Loan and Lease Losses, Write-offs	0	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts	0	0
Allowance for Loan and Lease Losses Write-offs, Net	0	0
Provision for Loan Losses Expensed	7	7
Allowance for Loan and Lease Losses, Adjustments, Other		0
Financing Receivable, Allowance for Credit Losses	138	128
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	21	24
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	117	104
Loans and Leases Receivable, Gross	41,326	42,402	$ 41,072
Financing Receivable, Individually Evaluated for Impairment	147	120
Financing Receivable, Collectively Evaluated for Impairment	$ 41,179	$ 42,282

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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- Definition

Amount of other addition (reduction) in allowance reserve for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Amount, after recoveries, of loans and leases that have been written-off.

+ References

No definition available.

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- References

No definition available.

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- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

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- Definition

Amount of expense related to loss from loan transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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