Quarterly Financial Statements (unaudited) Quarterly Financial Statements (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Statements (unaudited) [Abstract]
Net Financing Revenue	$ 976	$ 996	$ 984	$ 951	$ 983	$ 970	$ 916	$ 850	$ 3,907	$ 3,719	$ 3,375
Nonoperating Income (Expense)	392	388	374	376	356	332	211	243	1,530	1,142	1,276
Revenue, Net	1,368	1,384	1,358	1,327	1,339	1,302	1,127	1,093
Provision for Loan Losses Expensed	267	258	172	220	240	211	140	116	917	707	457
Noninterest Expense	721	735	773	710	668	674	724	695	2,939	2,761	2,948
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	380	391	413	397	431	417	263	282	1,581	1,393	1,246
Income Tax Expense (Benefit)	134	130	56	150	155	144	94	103	470	496	321
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	246	261	357	247	276	273	169	179	1,111	897	925
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	2	(52)	3	3	(13)	(5)	13	397	(44)	392	225
Net Income (Loss) Attributable to Parent	$ 248	$ 209	$ 360	$ 250	$ 263	$ 268	$ 182	$ 576	$ 1,067	$ 1,289	$ 1,150
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.52	$ 0.54	$ 0.70	$ 0.48	$ (1.94)	$ 0.49	$ (2.24)	$ 0.23	$ 2.25	$ (3.47)	$ 1.36
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.53	0.43	0.71	0.49	(1.97)	0.48	(2.22)	1.06	(0.09)	0.81	0.47
Income (Loss) from Continuing Operations, Per Diluted Share	0.52	0.54	0.70	0.48	(1.94)	0.49	(2.24)	0.23	2.24	(3.47)	1.36
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0.52	0.43	0.71	0.49	$ (1.97)	$ 0.47	$ (2.22)	$ 1.06	(0.09)	0.81	0.47
Common Stock, Dividends, Per Share, Declared	$ 0.08	$ 0.08	$ 0.00	$ 0.00					$ 0.16	$ 0.00	$ 0.00