Condensed Consolidated Statement of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Statement of Cash Flows [Abstract]
Net income	$ 1,337	$ 973
Net Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization	1,136	1,280
Provision for loan losses	722	652
Gain on mortgage and automotive loans, net	(22)	(19)
Other gain on investments, net	(174)	(37)
Originations and purchases of loans held-for-sale	(952)	(889)
Proceeds from sales and repayments of loans held-for-sale	788	830
Increase (decrease) in deferred income taxes	86	272
Increase (decrease) in interest payable	371	338
Increase (decrease) in other assets	(25)	(136)
Increase (decrease) in other liabilities	(98)	(9)
Increase (decrease) in other assets and liabilities, net	(36)	89
Net cash provided by operating activities	3,133	3,344
Net Cash (Used in) Provided by Investing Activities [Abstract]
Purchases of equity securities	(301)	(652)
Proceeds from sales of equity securities	615	715
Purchases of available-for-sale securities	11,214	5,669
Proceeds from sales of available-for-sale securities	5,699	637
Proceeds from repayments of available-for-sale securities	3,246	2,509
Purchases of held-to-maturity securities	(514)	(436)
Proceeds from repayments of held-to-maturity securities	195	107
Purchases of finance receivables and loans held-for-investment	(3,322)	(4,778)
Proceeds from sales of finance receivables and loans initially held-for-investment	427	53
Originations and repayments of finance receivables and loans held-for-investment and other, net	3,069	(558)
Purchases of operating lease assets	(2,937)	(2,991)
Disposals of operating lease assets	2,016	2,461
Net change in nonmarketable equity investments	179	(3)
Payments for (proceeds from) other, net	(306)	(241)
Net cash used in investing activities	(3,148)	(8,846)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net change in short-term borrowings	(4,652)	(4,074)
Net increase in deposits	13,032	8,063
Proceeds from issuance of long-term debt	5,438	14,756
Repayments of long-term debt	(14,114)	(12,994)
Repurchase of common stock	(740)	(630)
Dividends paid	(206)	(179)
Net cash (used in) provided by financing activities	(1,242)	4,942
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	2	(2)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Net decrease in cash and cash equivalents and restricted cash	(1,255)	(562)
Cash and cash equivalents and restricted cash [Roll Forward]
Cash and cash equivalents and restricted cash	5,626	5,269
Cash and cash equivalents and restricted cash	4,371	4,707
Supplemental Cash Flow Information [Abstract]
Cash paid for interest	2,781	2,242
Cash paid for income taxes	31	21
Held-to-maturity securities received in consideration for loans sold	0	26
Loans held-for-sale transferred to finance receivables and loans held-for-investment	125	0
Finance receivables and loans transferred to loans held-for-sale, noncash	964	815
Restricted Cash [Abstract]
Cash and cash equivalents as disclosed on the Condensed Consolidated Balance Sheet	3,617	3,772
Restricted cash included in other assets on the Condensed Consolidated Balance Sheet	$ 754	$ 935