Consolidated Statement of Income Consolidated Statement of Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Revenue and Other Income [Line Items]
Interest and Fee Income, Loans and Leases									$ 5,819	$ 5,162	$ 4,570
Interest and Fee Income, Loans and Leases Held-for-sale									0	0	40
Interest and Dividend Income, Securities, Operating, Available-for-sale									599	418	381
Interest Income, Deposits with Financial Institutions									37	14	8
Operating Leases, Income Statement, Lease Revenue									1,867	2,711	3,398
Total financing revenue and other interest income									8,322	8,305	8,397
Interest Expense [Abstract]
Interest Expense, Deposits									1,077	830	718
Interest Expense, Short-term Borrowings									127	57	49
Interest Expense, Long-term Debt									1,653	1,742	1,662
Interest Expense									2,857	2,629	2,429
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease									1,244	1,769	2,249
Net Financing Revenue	$ 1,094	$ 1,081	$ 1,067	$ 979	$ 976	$ 996	$ 984	$ 951	4,221	3,907	3,719
Other revenue [Abstract]
Insurance Services Revenue									973	945	940
Gain (Loss) on Sales of Loans, Net									68	11	45
Gain (Loss) on Extinguishment of Debt									(7)	(5)	(357)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments									102	185	155
Noninterest Income, Other Operating Income									408	394	359
Nonoperating Income (Expense)	379	381	388	396	392	388	374	376	1,544	1,530	1,142
Revenues									5,765	5,437	4,861
Provision for Loan Losses Expensed	294	314	269	271	267	258	172	220	1,148	917	707
Noninterest Expense [Abstract]
Labor and Related Expense									1,095	992	963
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims									332	342	293
Other Noninterest Expense									1,683	1,605	1,505
Noninterest Expense	769	753	810	778	721	735	773	710	3,110	2,939	2,761
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	410	395	376	326	380	391	413	397	1,507	1,581	1,393
Income Tax Expense (Benefit)	231	115	122	113	134	130	56	150	581	470	496
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	179	280	254	213	246	261	357	247	926	1,111	897
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	2	2	(2)	1	2	(52)	3	3	3	(44)	392
Net Income (Loss) Attributable to Parent	$ 181	$ 282	$ 252	$ 214	$ 248	$ 209	$ 360	$ 250	$ 929	$ 1,067	$ 1,289
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.40	$ 0.62	$ 0.55	$ 0.46	$ 0.52	$ 0.54	$ 0.70	$ 0.48	$ 2.04	$ 2.25	$ (3.47)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									0.01	(0.09)	0.81
Earnings Per Share, Basic	0.41	0.63	0.55	0.46	0.53	0.43	0.71	0.49	2.05	2.15	(2.66)
Earnings Per Share, Diluted [Abstract]
Income (Loss) from Continuing Operations, Per Diluted Share	0.40	0.62	0.55	0.46	0.52	0.54	0.70	0.48	2.03	2.24	(3.47)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share									0.01	(0.09)	0.81
Earnings Per Share, Diluted	0.41	0.63	0.55	0.46	0.52	0.43	0.71	0.49	2.04	2.15	(2.66)
Common Stock, Dividends, Per Share, Declared	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.00	$ 0.00	$ 0.40	$ 0.16	$ 0.00
Retained Earnings [Member]
Net Income (Loss) Attributable to Parent									$ 929	$ 1,067	$ 1,289