Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, noninterest-bearing	$ 946		$ 810
Cash and cash equivalents, interest-bearing	3,011		3,727
Cash and cash equivalents	3,957		4,537	$ 3,721
Equity securities	536		773
Available-for-sale securities	27,630		25,303
Held-to-maturity securities	2,387		2,362
Loans held-for-sale, net	107		314
Finance receivables and loans, net	130,055		129,926	125,327
Intercompany loans to nonbank subsidiary	0		0
Allowance for loan losses	1,288		1,242	1,278		$ 1,276
Total finance receivables and loans, net	128,767		128,684
Investment in operating leases, net	8,339		8,417
Intercompany receivables from bank subsidiary	0		0
Intercompany receivables from nonbank subsidiary	0		0
Investment in bank subsidiaries	0		0
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	2,401		2,326
Other assets	5,993		6,153
Assets	180,117		178,869	170,021
Deposit liabilities, noninterest-bearing	141		142
Deposit liabilities, interest-bearing	113,158		106,036
Deposit liabilities	113,299		106,178
Short-term borrowings	6,115		9,987
Long-term debt	41,490		44,193
Intercompany debt payable to bank subsidiaries	0		0
Intercompany debt payable to nonbank subsidiaries	0		0
Intercompany payables to bank subsidiary	0		0
Intercompany payables to nonbank subsidiaries	0		0
Interest payable	696		523
Unearned insurance premiums and service revenue	3,096		3,044
Accrued expenses and other liabilities	1,722		1,676
Total liabilities	166,418		165,601
Equity	13,699	$ 13,266	13,268	13,082	$ 13,375	$ 13,494
Total liabilities and equity	180,117		178,869
Parent
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, noninterest-bearing	45		55
Cash and cash equivalents, interest-bearing	14		5
Cash and cash equivalents	1,404		1,309	796
Equity securities	0		0
Available-for-sale securities	0		0
Held-to-maturity securities	0		0
Loans held-for-sale, net	0		0
Finance receivables and loans, net	2,109		2,349
Intercompany loans to nonbank subsidiary	372		882
Allowance for loan losses	36		55
Total finance receivables and loans, net	2,445		3,176
Investment in operating leases, net	3		5
Intercompany receivables from bank subsidiary	104		158
Intercompany receivables from nonbank subsidiary	46		45
Investment in bank subsidiaries	16,499		16,213
Investment in nonbank subsidiaries	6,687		6,928
Premiums receivable and other insurance assets	0		0
Other assets	2,292		2,226
Assets	29,480		30,060
Deposit liabilities, noninterest-bearing	0		0
Deposit liabilities, interest-bearing	0		1
Deposit liabilities	0		1
Short-term borrowings	2,486		2,477
Long-term debt	11,887		12,774
Intercompany debt payable to bank subsidiaries	17		20
Intercompany debt payable to nonbank subsidiaries	801		918
Intercompany payables to bank subsidiary	46		45
Intercompany payables to nonbank subsidiaries	108		124
Interest payable	218		159
Unearned insurance premiums and service revenue	0		0
Accrued expenses and other liabilities	218		274
Total liabilities	15,781		16,792
Equity	13,699		13,268
Total liabilities and equity	29,480		30,060
Guarantors
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, noninterest-bearing	0		0
Cash and cash equivalents, interest-bearing	0		0
Cash and cash equivalents	0		0	0
Equity securities	0		0
Available-for-sale securities	0		0
Held-to-maturity securities	0		0
Loans held-for-sale, net	0		0
Finance receivables and loans, net	0		0
Intercompany loans to nonbank subsidiary	0		0
Allowance for loan losses	0		0
Total finance receivables and loans, net	0		0
Investment in operating leases, net	0		0
Intercompany receivables from bank subsidiary	0		0
Intercompany receivables from nonbank subsidiary	0		0
Investment in bank subsidiaries	16,499		16,213
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	0		0
Other assets	0		0
Assets	16,499		16,213
Deposit liabilities, noninterest-bearing	0		0
Deposit liabilities, interest-bearing	0		0
Deposit liabilities	0		0
Short-term borrowings	0		0
Long-term debt	0		0
Intercompany debt payable to bank subsidiaries	0		0
Intercompany debt payable to nonbank subsidiaries	0		0
Intercompany payables to bank subsidiary	0		0
Intercompany payables to nonbank subsidiaries	0		0
Interest payable	0		0
Unearned insurance premiums and service revenue	0		0
Accrued expenses and other liabilities	0		0
Total liabilities	0		0
Equity	16,499		16,213
Total liabilities and equity	16,499		16,213
Nonguarantors
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, noninterest-bearing	901		755
Cash and cash equivalents, interest-bearing	2,997		3,722
Cash and cash equivalents	4,595		4,998	4,237
Equity securities	536		773
Available-for-sale securities	27,630		25,303
Held-to-maturity securities	2,404		2,382
Loans held-for-sale, net	107		314
Finance receivables and loans, net	127,928		127,577
Intercompany loans to nonbank subsidiary	104		397
Allowance for loan losses	1,252		1,187
Total finance receivables and loans, net	126,780		126,787
Investment in operating leases, net	8,336		8,412
Intercompany receivables from bank subsidiary	0		0
Intercompany receivables from nonbank subsidiary	110		129
Investment in bank subsidiaries	0		0
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	2,401		2,326
Other assets	5,440		5,453
Assets	178,339		176,877
Deposit liabilities, noninterest-bearing	141		142
Deposit liabilities, interest-bearing	113,158		106,035
Deposit liabilities	114,644		107,426
Short-term borrowings	3,629		7,510
Long-term debt	29,603		31,419
Intercompany debt payable to bank subsidiaries	0		0
Intercompany debt payable to nonbank subsidiaries	372		882
Intercompany payables to bank subsidiary	0		0
Intercompany payables to nonbank subsidiaries	113		129
Interest payable	478		364
Unearned insurance premiums and service revenue	3,096		3,044
Accrued expenses and other liabilities	3,236		2,962
Total liabilities	155,171		153,736
Equity	23,168		23,141
Total liabilities and equity	178,339		176,877
Affiliated entity
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, interest-bearing	0		0
Deposit liabilities, interest-bearing	0		0
Affiliated entity | Parent
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, interest-bearing	1,345		1,249
Deposit liabilities, interest-bearing	0		0
Affiliated entity | Guarantors
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, interest-bearing	0		0
Deposit liabilities, interest-bearing	0		0
Affiliated entity | Nonguarantors
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, interest-bearing	697		521
Deposit liabilities, interest-bearing	1,345		1,249
Consolidating adjustments
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, noninterest-bearing	0		0
Cash and cash equivalents, interest-bearing	0		0
Cash and cash equivalents	(2,042)		(1,770)	$ (1,312)
Equity securities	0		0
Available-for-sale securities	0		0
Held-to-maturity securities	(17)		(20)
Loans held-for-sale, net	0		0
Finance receivables and loans, net	18		0
Intercompany loans to nonbank subsidiary	(476)		(1,279)
Allowance for loan losses	0		0
Total finance receivables and loans, net	(458)		(1,279)
Investment in operating leases, net	0		0
Intercompany receivables from bank subsidiary	(104)		(158)
Intercompany receivables from nonbank subsidiary	(156)		(174)
Investment in bank subsidiaries	(32,998)		(32,426)
Investment in nonbank subsidiaries	(6,687)		(6,928)
Premiums receivable and other insurance assets	0		0
Other assets	(1,739)		(1,526)
Assets	(44,201)		(44,281)
Deposit liabilities, noninterest-bearing	0		0
Deposit liabilities, interest-bearing	0		0
Deposit liabilities	(1,345)		(1,249)
Short-term borrowings	0		0
Long-term debt	0		0
Intercompany debt payable to bank subsidiaries	(17)		(20)
Intercompany debt payable to nonbank subsidiaries	(1,173)		(1,800)
Intercompany payables to bank subsidiary	(46)		(45)
Intercompany payables to nonbank subsidiaries	(221)		(253)
Interest payable	0		0
Unearned insurance premiums and service revenue	0		0
Accrued expenses and other liabilities	(1,732)		(1,560)
Total liabilities	(4,534)		(4,927)
Equity	(39,667)		(39,354)
Total liabilities and equity	(44,201)		(44,281)
Consolidating adjustments | Affiliated entity
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents, interest-bearing	(2,042)		(1,770)
Deposit liabilities, interest-bearing	$ (1,345)		$ (1,249)