Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									$ 6,688	$ 5,819	$ 5,162
Interest on loans held-for-sale									15	0	0
Interest and dividends on investment securities and other earning assets									788	599	418
Interest on cash and cash equivalents									72	37	14
Operating leases									1,489	1,867	2,711
Financing revenue and other interest income									9,052	8,322	8,305
Interest on deposits									1,735	1,077	830
Interest on short-term borrowings									149	127	57
Interest on long-term debt									1,753	1,653	1,742
Interest on intercompany debt									0	0	0
Interest expense									3,637	2,857	2,629
Net depreciation expense on operating lease assets									1,025	1,244	1,769
Net financing (loss) revenue	$ 1,140	$ 1,107	$ 1,094	$ 1,049	$ 1,094	$ 1,081	$ 1,067	$ 979	4,390	4,221	3,907
Cash dividends from bank subsidiaries									0	0
Cash dividends from nonbank subsidiaries									0	0	0
Insurance premiums and service revenue earned									1,022	973	945
Gain on mortgage and automotive loans, net									25	68	11
Other (loss) gain on investments, net									(50)	102	185
Other income, net of losses									417	401	389
Other revenue	298	398	364	354	379	381	388	396	1,414	1,544	1,530
Net revenue									5,804	5,765	5,437
Provision for loan losses	266	233	158	261	294	314	269	271	918	1,148	917
Compensation and benefits expense									1,155	1,095	992
Insurance losses and loss adjustment expenses									295	332	342
Other operating expenses									1,814	1,683	1,605
Noninterest expense	804	807	839	814	769	753	810	778	3,264	3,110	2,939
Income from continuing operations before tax	368	465	461	328	410	395	376	326	1,622	1,507	1,581
Income tax expense from continuing operations	79	91	113	76	231	115	122	113	359	581	470
Net (loss) income from continuing operations	289	374	348	252	179	280	254	213	1,263	926	1,111
Income (loss) from discontinued operations, net of tax	1	0	1	(2)	2	2	(2)	1	0	3	(44)
Undistributed income of bank subsidiary									0	0	0
Undistributed income of nonbank subsidiaries									0	0	0
Net Income (Loss) Attributable to Parent	$ 290	$ 374	$ 349	$ 250	$ 181	$ 282	$ 252	$ 214	1,263	929	1,067
Other comprehensive income (loss), attributable to parent									(289)	106	(110)
Comprehensive income									974	1,035	957
Parent
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									(40)	(27)	(104)
Interest on loans held-for-sale									0
Interest and dividends on investment securities and other earning assets									0	0	0
Interest on cash and cash equivalents									8	7	5
Operating leases									5	11	17
Financing revenue and other interest income									(7)	7	(71)
Interest on deposits									0	3	8
Interest on short-term borrowings									44	60	40
Interest on long-term debt									1,009	1,101	1,161
Interest on intercompany debt									15	15	20
Interest expense									1,068	1,179	1,229
Net depreciation expense on operating lease assets									8	11	14
Net financing (loss) revenue									(1,083)	(1,183)	(1,314)
Cash dividends from bank subsidiaries									2,600	3,300
Cash dividends from nonbank subsidiaries									443	752	965
Insurance premiums and service revenue earned									0	0	0
Gain on mortgage and automotive loans, net									70	40	(11)
Other (loss) gain on investments, net									0	0	0
Other income, net of losses									411	675	1,250
Other revenue									481	715	1,239
Net revenue									2,441	3,584	890
Provision for loan losses									176	465	408
Compensation and benefits expense									83	180	573
Insurance losses and loss adjustment expenses									0	0	0
Other operating expenses									681	899	1,261
Noninterest expense									764	1,079	1,834
Income from continuing operations before tax									1,501	2,040	(1,352)
Income tax expense from continuing operations									(300)	337	(279)
Net (loss) income from continuing operations									1,801	1,703	(1,073)
Income (loss) from discontinued operations, net of tax									(2)	7	(39)
Undistributed income of bank subsidiary									(614)	(1,168)	1,273
Undistributed income of nonbank subsidiaries									78	387	906
Net Income (Loss) Attributable to Parent									1,263	929	1,067
Other comprehensive income (loss), attributable to parent									(289)	106	(110)
Comprehensive income									974	1,035	957
Guarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									0	0	0
Interest on loans held-for-sale									0
Interest and dividends on investment securities and other earning assets									0	0	0
Interest on cash and cash equivalents									0	0	0
Operating leases									0	0	0
Financing revenue and other interest income									0	0	0
Interest on deposits									0	0	0
Interest on short-term borrowings									0	0	0
Interest on long-term debt									0	0	0
Interest on intercompany debt									0	0	0
Interest expense									0	0	0
Net depreciation expense on operating lease assets									0	0	0
Net financing (loss) revenue									0	0	0
Cash dividends from bank subsidiaries									2,600	3,300
Cash dividends from nonbank subsidiaries									0	0	0
Insurance premiums and service revenue earned									0	0	0
Gain on mortgage and automotive loans, net									0	0	0
Other (loss) gain on investments, net									0	0	0
Other income, net of losses									0	0	0
Other revenue									0	0	0
Net revenue									2,600	3,300	0
Provision for loan losses									0	0	0
Compensation and benefits expense									0	0	0
Insurance losses and loss adjustment expenses									0	0	0
Other operating expenses									0	0	0
Noninterest expense									0	0	0
Income from continuing operations before tax									2,600	3,300	0
Income tax expense from continuing operations									0	0	(82)
Net (loss) income from continuing operations									2,600	3,300	82
Income (loss) from discontinued operations, net of tax									0	0	0
Undistributed income of bank subsidiary									(614)	(1,168)	1,273
Undistributed income of nonbank subsidiaries									0	0	(2)
Net Income (Loss) Attributable to Parent									1,986	2,132	1,353
Other comprehensive income (loss), attributable to parent									(243)	65	(63)
Comprehensive income									1,743	2,197	1,290
Nonguarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									6,728	5,846	5,266
Interest on loans held-for-sale									15
Interest and dividends on investment securities and other earning assets									789	601	421
Interest on cash and cash equivalents									64	30	9
Operating leases									1,484	1,856	2,694
Financing revenue and other interest income									9,094	8,346	8,407
Interest on deposits									1,735	1,078	822
Interest on short-term borrowings									105	67	17
Interest on long-term debt									744	552	581
Interest on intercompany debt									20	12	11
Interest expense									2,604	1,709	1,431
Net depreciation expense on operating lease assets									1,017	1,233	1,755
Net financing (loss) revenue									5,473	5,404	5,221
Cash dividends from bank subsidiaries									0	0
Cash dividends from nonbank subsidiaries									0	0	0
Insurance premiums and service revenue earned									1,022	973	945
Gain on mortgage and automotive loans, net									9	28	22
Other (loss) gain on investments, net									(50)	102	176
Other income, net of losses									770	834	935
Other revenue									1,751	1,937	2,078
Net revenue									7,224	7,341	7,299
Provision for loan losses									796	683	509
Compensation and benefits expense									1,072	915	419
Insurance losses and loss adjustment expenses									295	332	342
Other operating expenses									1,897	1,892	2,130
Noninterest expense									3,264	3,139	2,891
Income from continuing operations before tax									3,164	3,519	3,899
Income tax expense from continuing operations									659	244	831
Net (loss) income from continuing operations									2,505	3,275	3,068
Income (loss) from discontinued operations, net of tax									2	(4)	(5)
Undistributed income of bank subsidiary									0	0	0
Undistributed income of nonbank subsidiaries									0	0	0
Net Income (Loss) Attributable to Parent									2,507	3,271	3,063
Other comprehensive income (loss), attributable to parent									(308)	104	(106)
Comprehensive income									2,199	3,375	2,957
Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									0	0	0
Interest on cash and cash equivalents									0	0	0
Gain on mortgage and automotive loans, net									0	0	0
Affiliated entity | Parent
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									12	12	11
Interest on cash and cash equivalents									8	4	0
Gain on mortgage and automotive loans, net									(20)	2,068	877
Affiliated entity | Guarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									0	0	0
Interest on cash and cash equivalents									0	0	0
Gain on mortgage and automotive loans, net									0	0
Affiliated entity | Nonguarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									5	6	8
Interest on cash and cash equivalents									9	7	9
Gain on mortgage and automotive loans, net									(2)	217	(67)
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									0	0	0
Interest on loans held-for-sale									0
Interest and dividends on investment securities and other earning assets									(1)	(2)	(3)
Interest on cash and cash equivalents									0	0	0
Operating leases									0	0	0
Financing revenue and other interest income									(35)	(31)	(31)
Interest on deposits									0	(4)	0
Interest on short-term borrowings									0	0	0
Interest on long-term debt									0	0	0
Interest on intercompany debt									(35)	(27)	(31)
Interest expense									(35)	(31)	(31)
Net depreciation expense on operating lease assets									0	0	0
Net financing (loss) revenue									0	0	0
Cash dividends from bank subsidiaries									(5,200)	(6,600)
Cash dividends from nonbank subsidiaries									(443)	(752)	(965)
Insurance premiums and service revenue earned									0	0	0
Gain on mortgage and automotive loans, net									(54)	0	0
Other (loss) gain on investments, net									0	0	9
Other income, net of losses									(764)	(1,108)	(1,796)
Other revenue									(818)	(1,108)	(1,787)
Net revenue									(6,461)	(8,460)	(2,752)
Provision for loan losses									(54)	0	0
Compensation and benefits expense									0	0	0
Insurance losses and loss adjustment expenses									0	0	0
Other operating expenses									(764)	(1,108)	(1,786)
Noninterest expense									(764)	(1,108)	(1,786)
Income from continuing operations before tax									(5,643)	(7,352)	(966)
Income tax expense from continuing operations									0	0	0
Net (loss) income from continuing operations									(5,643)	(7,352)	(966)
Income (loss) from discontinued operations, net of tax									0	0	0
Undistributed income of bank subsidiary									1,228	2,336	(2,546)
Undistributed income of nonbank subsidiaries									(78)	(387)	(904)
Net Income (Loss) Attributable to Parent									(4,493)	(5,403)	(4,416)
Other comprehensive income (loss), attributable to parent									551	(169)	169
Comprehensive income									(3,942)	(5,572)	(4,247)
Consolidating adjustments | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									(17)	(18)	(19)
Interest on cash and cash equivalents									(17)	(11)	(9)
Gain on mortgage and automotive loans, net									$ 22	$ (2,285)	$ (810)