Securitizations and Variable Interest Entities (Schedule of Variable Interest Entities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Variable Interest Entity [Line Items]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale, Gain (Loss) on Sale	$ 0	$ 0	$ 0	$ 0
Total assets	185,270	$ 181,485	185,270	$ 181,485	$ 180,644
Liabilities	171,144		171,144		166,228
Held-to-maturity securities	1,255		1,255		1,568
Other assets	6,254		6,254		6,073
On-balance sheet variable interest entities
Variable Interest Entity [Line Items]
Total assets	15,151		15,151		19,344
Liabilities	5,875		5,875		9,098
Other assets	721		721		787
On-balance sheet variable interest entities | Consumer Automotive Industry Sector
Variable Interest Entity [Line Items]
Total assets	18,926		18,926		20,376
Liabilities	3,818		3,818		6,070
Assets Held-in-trust	9,700		9,700		9,000
Non-Recourse Debt	94		94		21
On-balance sheet variable interest entities | Commercial Automotive Industry Sector
Variable Interest Entity [Line Items]
Total assets	5,967		5,967		8,009
Liabilities	2,151		2,151		3,049
Off-balance sheet variable interest entities
Variable Interest Entity [Line Items]
Total assets	26,140		26,140		29,487
Liabilities	6,428		6,428		9,497
Assets sold to nonconsolidated VIEs	121		121		417
Maximum loss exposure to loss in nonconsolidated VIEs	1,746		1,746		1,837
Off-balance sheet variable interest entities | Consumer Automotive Industry Sector
Variable Interest Entity [Line Items]
Total assets	7		7		23
Liabilities	0		0		0
Assets sold to nonconsolidated VIEs	121		121		417
Maximum loss exposure to loss in nonconsolidated VIEs	128		128		440
Held-to-maturity securities	6		6		21
Other assets	1		1		2
Off-balance sheet variable interest entities | Commercial Other Industry Sector
Variable Interest Entity [Line Items]
Total assets	1,240		1,240		1,079
Liabilities	459		459		378
Assets sold to nonconsolidated VIEs	0		0		0
Maximum loss exposure to loss in nonconsolidated VIEs	1,618		1,618		1,397
Amount reconsolidated during the period | Consumer Automotive Industry Sector
Variable Interest Entity [Line Items]
Assets of nonconsolidated variable interest entity	$ 103		$ 103		$ 48