Consolidated Statement of Cash Flows $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 1,263	$ 929	$ 1,067
Depreciation and amortization	1,649	1,859	2,382
Provision for loan losses	918	1,148	917
Gain on mortgage and automotive loans, net	(25)	(68)	(11)
Other loss (gain) on investments, net	50	(102)	(185)
Originations and purchases of loans held-for-sale	(1,016)	(414)	(141)
Proceeds from sales and repayments of loans held-for-sale	948	310	240
Increase (decrease) in deferred income taxes	330	534	458
Increase (decrease) in interest payable	148	24	1
Increase (decrease) in other operating assets	(87)	(153)	(120)
Increase (decrease) in other operating liabilities	2	(69)	(206)
Increase (decrease) in other operating assets and liabilities, net	(30)	81	165
Net cash provided by (used in) operating activities	4,150	4,079	4,567
Net Cash (Used in) Provided by Investing Activities [Abstract]
Purchases of equity securities	(1,076)	(899)	(470)
Proceeds from sales of equity securities	787	1,049	680
Purchases of available-for-sale securities	(7,868)	(10,335)	(15,561)
Proceeds from sale of available-for-sale securities	852	3,584	10,356
Proceeds from repayments of available-for-sale securities	3,215	2,899	3,379
Purchases of held-to-maturity securities	(578)	(1,026)	(841)
Proceeds from repayments of held-to-maturity securities	147	68	0
Purchases of finance receivables and loans held-for-investment	(5,693)	(5,452)	(3,859)
Proceeds from sales of finance receivables and loans initially held-for-investment	91	1,339	4,285
Originations and repayments of finance receivables and loans held-for-investment and other, net	(3,245)	(1,063)	(8,826)
Purchases of operating lease assets	(3,709)	(4,052)	(3,274)
Disposals of operating lease assets	3,089	5,567	6,304
Acquisitions, net of cash acquired	0	0	309
Net change in nonmarketable equity investments	(181)	(187)	(628)
Payments for (proceeds from) other, net	(340)	(219)	(306)
Net cash provided by investing activities	(14,509)	(8,727)	(9,070)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net change in short-term borrowings	(1,426)	(1,263)	4,564
Net increase in deposits	12,867	14,172	12,508
Proceeds from issuance of long-term debt	18,401	17,969	14,155
Repayments of long-term debt	(17,940)	(27,908)	(26,412)
Repurchase and redemption of preferred stock	0	0	696
Repurchase of common stock	(939)	(753)	(341)
Dividends paid	(242)	(184)	(108)
Net cash provided by (used in) financing activities	10,721	2,033	3,670
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	(5)	3	1
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Net increase (decrease) in cash and cash equivalents and restricted cash	357	(2,612)	(832)
Cash and cash equivalents and restricted cash	5,626	5,269	7,881
Cash and cash equivalents as disclosed on the Consolidated Balance Sheet	4,537	4,252
Restricted cash included in other assets on the Consolidated Balance Sheet	1,089	1,017
Supplemental Cash Flow Information [Abstract]
Cash paid for interest	3,380	2,829	2,647
Cash paid for income taxes	36	51	19
Held-to-maturity securities received in consideration for loans sold, noncash	26	56	0
Finance receivables and loans transferred to loans held-for-sale, noncash	815	1,339	4,282
Proceeds from repayments of mortgage loans held-for-investment originally designated as held-for-sale	$ 23	$ 36	$ 40