Parent and Guarantor Condensed Consolidating Financial Statements (Statement of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	$ 1,081	$ 1,097
Purchases of equity securities	(48)	(374)
Proceeds from sales of equity securities	383	220
Purchases of available-for-sale securities	(3,401)	(2,360)
Proceeds from sale of available-for-sale securities	656	328
Proceeds from repayments of available-for-sale securities	694	795
Purchases of held-to-maturity securities	(131)	(155)
Proceeds from repayments of held-to-maturity securities	44	35
Purchases of finance receivables and loans held-for-investment	(1,452)	(1,497)
Proceeds from sales of finance receivables and loans initially held-for-investment	157	0
Originations and repayments of finance receivables and loans held-for-investment and other, net	1,149	(1,300)
Net change in intercompany loans	10	1
Purchases of operating lease assets	(792)	(969)
Disposals of operating lease assets	624	976
Capital contributions to subsidiaries	0	0
Returns of contributed capital	0	0
Net change in nonmarketable equity investments	171	(19)
Payments for (proceeds from) other, net	(95)	(82)
Net cash provided by investing activities	(2,041)	(4,402)
Net change in short-term borrowings	(3,872)	(1,848)
Net (decrease) increase in deposits	7,114	4,173
Proceeds from issuance of long-term debt	1,766	6,665
Repayments of long-term debt	(4,490)	(5,771)
Repurchase of common stock	(211)	(185)
Dividends paid	(70)	(58)
Capital contributions from parent	0	0
Net cash provided by (used in) financing activities	237	2,976
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	1	(2)
Net increase (decrease) in cash and cash equivalents and restricted cash	(722)	(331)
Cash and cash equivalents and restricted cash	4,904	4,938	$ 5,626	$ 5,269
Cash and cash equivalents	3,957	3,721	4,537
Restricted cash included in other assets on the Condensed Consolidated Balance Sheet	947	1,217
Parent
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	155	456
Purchases of equity securities	0	0
Proceeds from sales of equity securities	0	0
Purchases of available-for-sale securities	0	0
Proceeds from sale of available-for-sale securities	0	0
Proceeds from repayments of available-for-sale securities	0	0
Purchases of held-to-maturity securities	0	0
Proceeds from repayments of held-to-maturity securities	0	0
Purchases of finance receivables and loans held-for-investment	0	0
Proceeds from sales of finance receivables and loans initially held-for-investment	402	820
Originations and repayments of finance receivables and loans held-for-investment and other, net	301	432
Net change in intercompany loans	4	28
Purchases of operating lease assets	0	0
Disposals of operating lease assets	1	4
Capital contributions to subsidiaries	(1)	(49)
Returns of contributed capital	15	38
Net change in nonmarketable equity investments	(1)	0
Payments for (proceeds from) other, net	0	(3)
Net cash provided by investing activities	1,224	819
Net change in short-term borrowings	9	(214)
Net (decrease) increase in deposits	(1)	(6)
Proceeds from issuance of long-term debt	7	15
Repayments of long-term debt	(900)	(1,152)
Repurchase of common stock	(211)	(185)
Dividends paid	(70)	(58)
Capital contributions from parent	0	0
Net cash provided by (used in) financing activities	(1,284)	(1,727)
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	0	0
Net increase (decrease) in cash and cash equivalents and restricted cash	95	(452)
Cash and cash equivalents and restricted cash	1,493	943	1,398	1,395
Cash and cash equivalents	1,404	796	1,309
Restricted cash included in other assets on the Condensed Consolidated Balance Sheet	89	147
Guarantors
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	400	1,000
Purchases of equity securities	0	0
Proceeds from sales of equity securities	0	0
Purchases of available-for-sale securities	0	0
Proceeds from sale of available-for-sale securities	0	0
Proceeds from repayments of available-for-sale securities	0	0
Purchases of held-to-maturity securities	0	0
Proceeds from repayments of held-to-maturity securities	0	0
Purchases of finance receivables and loans held-for-investment	0	0
Proceeds from sales of finance receivables and loans initially held-for-investment	0	0
Originations and repayments of finance receivables and loans held-for-investment and other, net	0	0
Net change in intercompany loans	0	0
Purchases of operating lease assets	0	0
Disposals of operating lease assets	0	0
Capital contributions to subsidiaries	0	(6)
Returns of contributed capital	0	0
Net change in nonmarketable equity investments	0	0
Payments for (proceeds from) other, net	0	0
Net cash provided by investing activities	0	(6)
Net change in short-term borrowings	0	0
Net (decrease) increase in deposits	0	0
Proceeds from issuance of long-term debt	0	0
Repayments of long-term debt	0	0
Repurchase of common stock	0	0
Dividends paid	0	0
Capital contributions from parent	0	6
Net cash provided by (used in) financing activities	(400)	(994)
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	0	0
Net increase (decrease) in cash and cash equivalents and restricted cash	0	0
Cash and cash equivalents and restricted cash	0	0	0	0
Cash and cash equivalents	0	0	0
Restricted cash included in other assets on the Condensed Consolidated Balance Sheet	0	0
Nonguarantors
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	1,369	1,812
Purchases of equity securities	(48)	(374)
Proceeds from sales of equity securities	383	220
Purchases of available-for-sale securities	(3,401)	(2,360)
Proceeds from sale of available-for-sale securities	656	328
Proceeds from repayments of available-for-sale securities	694	795
Purchases of held-to-maturity securities	(131)	(155)
Proceeds from repayments of held-to-maturity securities	44	35
Purchases of finance receivables and loans held-for-investment	(1,843)	(2,317)
Proceeds from sales of finance receivables and loans initially held-for-investment	146	0
Originations and repayments of finance receivables and loans held-for-investment and other, net	848	(1,732)
Net change in intercompany loans	6	1
Purchases of operating lease assets	(792)	(969)
Disposals of operating lease assets	623	972
Capital contributions to subsidiaries	0	0
Returns of contributed capital	0	0
Net change in nonmarketable equity investments	172	(19)
Payments for (proceeds from) other, net	(94)	(80)
Net cash provided by investing activities	(2,450)	(5,646)
Net change in short-term borrowings	(3,881)	(1,634)
Net (decrease) increase in deposits	7,211	3,776
Proceeds from issuance of long-term debt	1,759	6,650
Repayments of long-term debt	(3,590)	(4,619)
Repurchase of common stock	0	0
Dividends paid	0	0
Capital contributions from parent	1	49
Net cash provided by (used in) financing activities	535	3,436
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	1	(2)
Net increase (decrease) in cash and cash equivalents and restricted cash	(545)	(400)
Cash and cash equivalents and restricted cash	5,453	5,307	5,998	5,707
Cash and cash equivalents	4,595	4,237	4,998
Restricted cash included in other assets on the Condensed Consolidated Balance Sheet	858	1,070
Consolidating adjustments
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net cash provided by (used in) operating activities	(843)	(2,171)
Purchases of equity securities	0	0
Proceeds from sales of equity securities	0	0
Purchases of available-for-sale securities	0	0
Proceeds from sale of available-for-sale securities	0	0
Proceeds from repayments of available-for-sale securities	0	0
Purchases of held-to-maturity securities	0	0
Proceeds from repayments of held-to-maturity securities	0	0
Purchases of finance receivables and loans held-for-investment	391	820
Proceeds from sales of finance receivables and loans initially held-for-investment	(391)	(820)
Originations and repayments of finance receivables and loans held-for-investment and other, net	0	0
Net change in intercompany loans	0	(28)
Purchases of operating lease assets	0	0
Disposals of operating lease assets	0	0
Capital contributions to subsidiaries	1	55
Returns of contributed capital	(15)	(38)
Net change in nonmarketable equity investments	0	0
Payments for (proceeds from) other, net	(1)	1
Net cash provided by investing activities	(815)	431
Net change in short-term borrowings	0	0
Net (decrease) increase in deposits	(96)	403
Proceeds from issuance of long-term debt	0	0
Repayments of long-term debt	0	0
Repurchase of common stock	0	0
Dividends paid	0	0
Capital contributions from parent	(1)	(55)
Net cash provided by (used in) financing activities	1,386	2,261
Effect of exchange-rate changes on cash and cash equivalents and restricted cash	0	0
Net increase (decrease) in cash and cash equivalents and restricted cash	(272)	521
Cash and cash equivalents and restricted cash	(2,042)	(1,312)	(1,770)	$ (1,833)
Cash and cash equivalents	(2,042)	(1,312)	$ (1,770)
Restricted cash included in other assets on the Condensed 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
Net change in intercompany debt	0	0
Dividends paid and returns of contributed capital, intercompany	0	0
Affiliated entity | Parent
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net change in intercompany investment securities	0	0
Net change in intercompany loans	507	(423)
Net change in intercompany debt	(118)	(127)
Dividends paid and returns of contributed capital, intercompany	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
Dividends paid and returns of contributed capital, intercompany	(400)	(1,000)
Affiliated entity | Nonguarantors
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net change in intercompany investment securities	3	9
Net change in intercompany loans	290	1
Net change in intercompany debt	(507)	422
Dividends paid and returns of contributed capital, intercompany	(458)	(1,208)
Affiliated entity | Consolidating adjustments
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net change in intercompany investment securities	(3)	(9)
Net change in intercompany loans	(797)	422
Net change in intercompany debt	625	(295)
Dividends paid and returns of contributed capital, intercompany	$ 858	$ 2,208