Securitizations and Variable Interest Entities (Schedule of Variable Interest Entities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount	$ 1
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale, Gain (Loss) on Sale	0	$ 0	$ 1
Total assets	182,165	180,644	$ 178,869
Liabilities	167,462	166,228
Held-to-maturity securities	1,253	1,568
Other assets	6,415	6,073
On-balance sheet variable interest entities
Variable Interest Entity [Line Items]
Total assets	14,196	19,344
Liabilities	4,161	9,098
Other assets	983	787
On-balance sheet variable interest entities | Consumer Automotive Industry Sector
Variable Interest Entity [Line Items]
Total assets	17,833	20,376
Liabilities	3,103	6,070
Assets Held-in-trust	9,900	9,000
Non-Recourse Debt	94	21
On-balance sheet variable interest entities | Commercial Automotive Industry Sector
Variable Interest Entity [Line Items]
Total assets	6,276	8,009
Liabilities	1,152	3,049
Off-balance sheet variable interest entities
Variable Interest Entity [Line Items]
Total assets	25,404	29,487
Liabilities	4,784	9,497
Assets sold to nonconsolidated VIEs	0	417
Maximum loss exposure to loss in nonconsolidated VIEs	1,754	1,837
Off-balance sheet variable interest entities | Consumer Automotive Industry Sector
Variable Interest Entity [Line Items]
Total assets	0	23
Liabilities	0	0
Assets sold to nonconsolidated VIEs	0	417
Maximum loss exposure to loss in nonconsolidated VIEs	0	440
Held-to-maturity securities		21
Other assets		2
Off-balance sheet variable interest entities | Commercial Other Industry Sector
Variable Interest Entity [Line Items]
Total assets	1,295	1,079
Liabilities	529	378
Assets sold to nonconsolidated VIEs	0	0
Maximum loss exposure to loss in nonconsolidated VIEs	1,754	1,397
Amount reconsolidated during the period | Consumer Automotive Industry Sector
Variable Interest Entity [Line Items]
Assets of nonconsolidated variable interest entity	$ 103	$ 48