Parent and Guarantor Condensed Consolidating Financial Statements (Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	$ 4,150	$ 4,079	$ 4,567
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)
Net change in intercompany loans	25	68	11
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)
Capital contributions to subsidiaries	0	0	0
Returns of contributed capital	0	0	0
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 change in short-term borrowings	(1,426)	(1,263)	4,564
Net (decrease) 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)
Redemption of preferred stock			(696)
Repurchase of common stock	(939)	(753)	(341)
Dividends paid	(242)	(184)	(108)
Capital contributions from parent	0	0	0
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
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	$ 8,713
Cash and cash equivalents	4,537	4,252
Restricted cash included in other assets on the Consolidated Balance Sheet	1,089	1,017
Parent
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	1,659	4,591	241
Purchases of equity securities	0	0	0
Proceeds from sales of equity securities	0	0	0
Purchases of available-for-sale securities	0	0	0
Proceeds from sale of available-for-sale securities	0	0	0
Proceeds from repayments of available-for-sale securities	0	0	0
Purchases of held-to-maturity securities	0	0	0
Proceeds from repayments of held-to-maturity securities	0	0
Purchases of finance receivables and loans held-for-investment	(131)	(35)	(4)
Proceeds from sales of finance receivables and loans initially held-for-investment	1,596	106	0
Originations and repayments of finance receivables and loans held-for-investment and other, net	3,489	860	2,013
Net change in intercompany loans	70	40	(11)
Purchases of operating lease assets	0	0	0
Disposals of operating lease assets	10	13	25
Acquisitions, net of cash acquired			(309)
Capital contributions to subsidiaries	(61)	(1,212)	(3,908)
Returns of contributed capital	266	1,567	3,678
Net change in nonmarketable equity investments	(16)	0	0
Payments for (proceeds from) other, net	0	(31)	(206)
Net cash provided by investing activities	5,133	3,343	2,166
Net change in short-term borrowings	(694)	(453)	169
Net (decrease) increase in deposits	(11)	(156)	(61)
Proceeds from issuance of long-term debt	69	354	979
Repayments of long-term debt	(4,774)	(6,111)	(2,662)
Redemption of preferred stock			(696)
Repurchase of common stock	(939)	(753)	(341)
Dividends paid	(242)	(184)	(108)
Capital contributions from parent	0	0	0
Net cash provided by (used in) financing activities	(6,789)	(7,528)	(3,102)
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	0	0	0
Net increase (decrease) in cash and cash equivalents and restricted cash	3	406	(695)
Cash and cash equivalents and restricted cash	1,398	1,395	989	1,684
Cash and cash equivalents	1,309	1,217
Restricted cash included in other assets on the Consolidated Balance Sheet	89	178
Guarantors
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	2,600	3,300	6
Purchases of equity securities	0	0	0
Proceeds from sales of equity securities	0	0	0
Purchases of available-for-sale securities	0	0	0
Proceeds from sale of available-for-sale securities	0	0	0
Proceeds from repayments of available-for-sale securities	0	0	0
Purchases of held-to-maturity securities	0	0	0
Proceeds from repayments of held-to-maturity securities	0	0
Purchases of finance receivables and loans held-for-investment	0	0	0
Proceeds from sales of finance receivables and loans initially held-for-investment	0	0	0
Originations and repayments of finance receivables and loans held-for-investment and other, net	0	0	0
Net change in intercompany loans	0	0	0
Purchases of operating lease assets	0	0	0
Disposals of operating lease assets	0	0	0
Acquisitions, net of cash acquired			0
Capital contributions to subsidiaries	(6)	(5)	0
Returns of contributed capital	0	0	8
Net change in nonmarketable equity investments	0	0	0
Payments for (proceeds from) other, net	0	0	0
Net cash provided by investing activities	(6)	(5)	8
Net change in short-term borrowings	0	0	0
Net (decrease) increase in deposits	0	0	0
Proceeds from issuance of long-term debt	0	0	0
Repayments of long-term debt	0	0	0
Redemption of preferred stock			0
Repurchase of common stock	0	0	0
Dividends paid	0	0	0
Capital contributions from parent	6	5	0
Net cash provided by (used in) financing activities	(2,594)	(3,295)	(14)
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	0	0	0
Net increase (decrease) in cash and cash equivalents and restricted cash	0	0	0
Cash and cash equivalents and restricted cash	0	0	0	0
Cash and cash equivalents	0	0
Restricted cash included in other assets on the Consolidated Balance Sheet	0	0
Nonguarantors
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	5,536	3,466	5,383
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
Purchases of finance receivables and loans held-for-investment	(7,101)	(5,417)	(3,855)
Proceeds from sales of finance receivables and loans initially held-for-investment	34	1,233	4,285
Originations and repayments of finance receivables and loans held-for-investment and other, net	(6,734)	33	(10,839)
Net change in intercompany loans	9	28	22
Purchases of operating lease assets	(3,709)	(4,052)	(3,274)
Disposals of operating lease assets	3,079	5,554	6,279
Acquisitions, net of cash acquired			0
Capital contributions to subsidiaries	0	0	0
Returns of contributed capital	0	0	0
Net change in nonmarketable equity investments	(165)	(187)	(628)
Payments for (proceeds from) other, net	(340)	(99)	(191)
Net cash provided by investing activities	(19,405)	(7,087)	(10,747)
Net change in short-term borrowings	(732)	(810)	4,395
Net (decrease) increase in deposits	12,989	15,466	12,569
Proceeds from issuance of long-term debt	18,332	15,654	13,176
Repayments of long-term debt	(13,166)	(21,797)	(23,750)
Redemption of preferred stock			0
Repurchase of common stock	0	0	0
Dividends paid	0	0	0
Capital contributions from parent	61	1,212	3,908
Net cash provided by (used in) financing activities	14,165	2,032	4,777
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	(5)	3	1
Net increase (decrease) in cash and cash equivalents and restricted cash	291	(1,586)	(586)
Cash and cash equivalents and restricted cash	5,998	5,707	7,293	7,879
Cash and cash equivalents	4,998	4,868
Restricted cash included in other assets on the Consolidated Balance Sheet	1,000	839
Consolidating adjustments
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	(5,645)	(7,278)	(1,063)
Purchases of equity securities	0	0	0
Proceeds from sales of equity securities	0	0	0
Purchases of available-for-sale securities	0	0	0
Proceeds from sale of available-for-sale securities	0	0	0
Proceeds from repayments of available-for-sale securities	0	0	0
Purchases of held-to-maturity securities	0	0	0
Proceeds from repayments of held-to-maturity securities	0	0
Purchases of finance receivables and loans held-for-investment	1,539	0	0
Proceeds from sales of finance receivables and loans initially held-for-investment	(1,539)	0	0
Originations and repayments of finance receivables and loans held-for-investment and other, net	0	(1,956)	0
Net change in intercompany loans	(54)	0	0
Purchases of operating lease assets	0	0	0
Disposals of operating lease assets	0	0	0
Acquisitions, net of cash acquired			0
Capital contributions to subsidiaries	67	1,217	3,908
Returns of contributed capital	(266)	(1,567)	(3,686)
Net change in nonmarketable equity investments	0	0	0
Payments for (proceeds from) other, net	0	(89)	91
Net cash provided by investing activities	(231)	(4,978)	(497)
Net change in short-term borrowings	0	0	0
Net (decrease) increase in deposits	(111)	(1,138)	0
Proceeds from issuance of long-term debt	0	1,961	0
Repayments of long-term debt	0	0	0
Redemption of preferred stock			0
Repurchase of common stock	0	0	0
Dividends paid	0	0	0
Capital contributions from parent	(67)	(1,217)	(3,908)
Net cash provided by (used in) financing activities	5,939	10,824	2,009
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	0	0	0
Net increase (decrease) in cash and cash equivalents and restricted cash	63	(1,432)	449
Cash and cash equivalents and restricted cash	(1,770)	(1,833)	(401)	$ (850)
Cash and cash equivalents	(1,770)	(1,833)
Restricted cash included in other assets on the Consolidated Balance Sheet	0	0
Affiliated entity
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net change in intercompany investment securities	0	0
Net change in intercompany loans	0	0	0
Net change in intercompany debt	0	0	0
Dividends paid and returns of contributed capital, intercompany	0	0	0
Affiliated entity | Parent
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net change in intercompany investment securities	0	7
Net change in intercompany loans	(20)	2,068	877
Net change in intercompany debt	(198)	(225)	(382)
Dividends paid and returns of contributed capital, intercompany	0	0	0
Affiliated entity | Guarantors
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net change in intercompany investment securities	0	0
Net change in intercompany loans	0	0
Net change in intercompany debt	0	0	0
Dividends paid and returns of contributed capital, intercompany	(2,600)	(3,300)	(14)
Affiliated entity | Nonguarantors
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net change in intercompany investment securities	54	291
Net change in intercompany loans	(2)	217	(67)
Net change in intercompany debt	(10)	(2,074)	(877)
Dividends paid and returns of contributed capital, intercompany	(3,309)	(5,619)	(4,644)
Affiliated entity | Consolidating adjustments
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net change in intercompany investment securities	(54)	(298)
Net change in intercompany loans	22	(2,285)	(810)
Net change in intercompany debt	208	2,299	1,259
Dividends paid and returns of contributed capital, intercompany	$ 5,909	$ 8,919	$ 4,658