Parent and Guarantor Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 4,079	$ 4,567	$ 5,111
Payments to Acquire Available-for-sale Securities	(11,234)	(16,031)	(12,250)
Proceeds from sales of available-for-sale securities	4,633	11,036	6,874
Proceeds from maturities and repayment of available-for-sale securities	2,899	3,379	4,255
Payments to Acquire Held-to-maturity Securities	(1,026)	(841)	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	68	0	0
Payments to Acquire Loans Held-for-investment	(5,452)	(3,859)	(4,501)
Proceeds from Sale of Loans and Leases Held-for-investment	1,339	4,285	3,197
Originations and repayments of loans held-for-investment and other	(1,063)	(8,826)	(9,344)
Purchases of operating lease assets	(4,052)	(3,274)	(4,685)
Disposals of operating lease assets	5,567	6,304	5,546
Payments to Acquire Interest in Subsidiaries and Affiliates	0	309	0
Proceeds from Contributions from Parent	0	0	0
Returns of contributed capital	0	0	0
Proceeds from Divestiture of Businesses	0	0	1,049
Increase (Decrease) in Non marketable equity securities	(187)	(628)	(147)
Payments for (Proceeds from) Other Investing Activities	(219)	(306)	3
Net cash provided by investing activities	(8,727)	(9,070)	(10,003)
Proceeds from (Repayments of) Short-term Debt	(1,263)	4,564	1,028
Increase (Decrease) in Deposits	14,172	12,508	8,247
Proceeds from issuance of long-term debt	17,969	14,155	30,665
Repayments of long-term debt	(27,908)	(26,412)	(31,350)
Net Change in Debt, Intercompany	0	0	0
Payments for Repurchase of Redeemable Preferred Stock	0	(696)	(559)
Payments for Repurchase of Common Stock	(753)	(341)	(16)
Payments of Dividends	(184)	(108)	(2,571)
Dividends paid and returns of contributed capital, Intercompany	0	0	0
Capital contributions from parent	0	0	0
Net cash (used in) provided by financing activities	2,033	3,670	5,444
Effect of exchange-rate changes on cash and cash equivalents	3	1	(4)
Cash and Cash Equivalents, Period Increase (Decrease)	(2,612)	(832)	548
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	5,269	7,881	8,713	$ 8,165
Restricted Cash	1,017	1,947
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	4,591	241	370
Payments to Acquire Available-for-sale Securities	0	0	0
Proceeds from sales of available-for-sale securities	0	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0
Payments to Acquire Loans Held-for-investment	(35)	(4)	(169)
Proceeds from Sale of Loans and Leases Held-for-investment	106	0	0
Originations and repayments of loans held-for-investment and other	860	2,013	1,954
Purchases of operating lease assets	0	0	(94)
Disposals of operating lease assets	13	25	7
Payments to Acquire Interest in Subsidiaries and Affiliates		309
Proceeds from Contributions from Parent	(1,212)	(3,908)	(796)
Returns of contributed capital	1,567	3,678	1,444
Proceeds from Divestiture of Businesses			1,049
Increase (Decrease) in Non marketable equity securities	0	0	0
Payments for (Proceeds from) Other Investing Activities	(31)	(206)	(47)
Net cash provided by investing activities	3,343	2,166	3,588
Proceeds from (Repayments of) Short-term Debt	(453)	169	115
Increase (Decrease) in Deposits	(156)	(61)	(91)
Proceeds from issuance of long-term debt	354	979	5,428
Repayments of long-term debt	(6,111)	(2,662)	(5,931)
Net Change in Debt, Intercompany	(225)	(382)	(977)
Payments for Repurchase of Redeemable Preferred Stock		(696)	(559)
Payments for Repurchase of Common Stock	(753)	(341)	(16)
Payments of Dividends	(184)	(108)	(2,571)
Dividends paid and returns of contributed capital, Intercompany	0	0	0
Capital contributions from parent	0	0	0
Net cash (used in) provided by financing activities	(7,528)	(3,102)	(4,602)
Effect of exchange-rate changes on cash and cash equivalents	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	406	(695)	(644)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1,395	989	1,684	2,328
Restricted Cash	178	169
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	3,300	6	525
Payments to Acquire Available-for-sale Securities	0	0	0
Proceeds from sales of available-for-sale securities	0	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0
Payments to Acquire Loans Held-for-investment	0	0	0
Proceeds from Sale of Loans and Leases Held-for-investment	0	0	0
Originations and repayments of loans held-for-investment and other	0	0	0
Purchases of operating lease assets	0	0	0
Disposals of operating lease assets	0	0	0
Payments to Acquire Interest in Subsidiaries and Affiliates		0
Proceeds from Contributions from Parent	(5)	0	(1)
Returns of contributed capital	0	8	0
Proceeds from Divestiture of Businesses			0
Increase (Decrease) in Non marketable equity securities	0	0	0
Payments for (Proceeds from) Other Investing Activities	0	0	0
Net cash provided by investing activities	(5)	8	(1)
Proceeds from (Repayments of) Short-term Debt	0	0	0
Increase (Decrease) in Deposits	0	0	0
Proceeds from issuance of long-term debt	0	0	0
Repayments of long-term debt	0	0	0
Net Change in Debt, Intercompany	0	0	0
Payments for Repurchase of Redeemable Preferred Stock		0	0
Payments for Repurchase of Common Stock	0	0	0
Payments of Dividends	0	0	0
Dividends paid and returns of contributed capital, Intercompany	(3,300)	(14)	(525)
Capital contributions from parent	5	0	1
Net cash (used in) provided by financing activities	(3,295)	(14)	(524)
Effect of exchange-rate changes on cash and cash equivalents	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	0	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0	0
Restricted Cash	0	0
Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	3,466	5,383	6,390
Payments to Acquire Available-for-sale Securities	(11,234)	(16,031)	(12,250)
Proceeds from sales of available-for-sale securities	4,633	11,036	6,874
Proceeds from maturities and repayment of available-for-sale securities	2,899	3,379	4,255
Payments to Acquire Held-to-maturity Securities	(1,026)	(841)
Proceeds from Sale and Maturity of Held-to-maturity Securities	68
Payments to Acquire Loans Held-for-investment	(5,417)	(3,855)	(4,332)
Proceeds from Sale of Loans and Leases Held-for-investment	1,233	4,285	3,197
Originations and repayments of loans held-for-investment and other	33	(10,839)	(11,298)
Purchases of operating lease assets	(4,052)	(3,274)	(4,591)
Disposals of operating lease assets	5,554	6,279	5,539
Payments to Acquire Interest in Subsidiaries and Affiliates		0
Proceeds from Contributions from Parent	0	0	0
Returns of contributed capital	0	0	0
Proceeds from Divestiture of Businesses			0
Increase (Decrease) in Non marketable equity securities	(187)	(628)	(147)
Payments for (Proceeds from) Other Investing Activities	(99)	(191)	50
Net cash provided by investing activities	(7,087)	(10,747)	(11,492)
Proceeds from (Repayments of) Short-term Debt	(810)	4,395	913
Increase (Decrease) in Deposits	15,466	12,569	8,338
Proceeds from issuance of long-term debt	15,654	13,176	25,237
Repayments of long-term debt	(21,797)	(23,750)	(25,419)
Net Change in Debt, Intercompany	(2,074)	(877)	(240)
Payments for Repurchase of Redeemable Preferred Stock		0	0
Payments for Repurchase of Common Stock	0	0	0
Payments of Dividends	0	0	0
Dividends paid and returns of contributed capital, Intercompany	(5,619)	(4,644)	(3,092)
Capital contributions from parent	1,212	3,908	796
Net cash (used in) provided by financing activities	2,032	4,777	6,533
Effect of exchange-rate changes on cash and cash equivalents	3	1	(4)
Cash and Cash Equivalents, Period Increase (Decrease)	(1,586)	(586)	1,427
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	5,707	7,293	7,879	6,452
Restricted Cash	839	1,778
Affiliated Entity [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	0
Payments for (Proceeds from) Loans and Leases	0	0	0
Affiliated Entity [Member] | Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	(7)
Payments for (Proceeds from) Loans and Leases	2,068	877	240
Affiliated Entity [Member] | Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	0
Payments for (Proceeds from) Loans and Leases	0	0	0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	(291)
Payments for (Proceeds from) Loans and Leases	217	(67)	1,211
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(7,278)	(1,063)	(2,174)
Payments to Acquire Available-for-sale Securities	0	0	0
Proceeds from sales of available-for-sale securities	0	0	0
Proceeds from maturities and repayment of available-for-sale securities	0	0	0
Payments to Acquire Held-to-maturity Securities	0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities	0
Payments to Acquire Loans Held-for-investment	0	0	0
Proceeds from Sale of Loans and Leases Held-for-investment	0	0	0
Originations and repayments of loans held-for-investment and other	(1,956)	0	0
Purchases of operating lease assets	0	0	0
Disposals of operating lease assets	0	0	0
Payments to Acquire Interest in Subsidiaries and Affiliates		0
Proceeds from Contributions from Parent	1,217	3,908	797
Returns of contributed capital	(1,567)	(3,686)	(1,444)
Proceeds from Divestiture of Businesses			0
Increase (Decrease) in Non marketable equity securities	0	0	0
Payments for (Proceeds from) Other Investing Activities	(89)	91	0
Net cash provided by investing activities	(4,978)	(497)	(2,098)
Proceeds from (Repayments of) Short-term Debt	0	0	0
Increase (Decrease) in Deposits	(1,138)	0	0
Proceeds from issuance of long-term debt	1,961	0	0
Repayments of long-term debt	0	0	0
Net Change in Debt, Intercompany	2,299	1,259	1,217
Payments for Repurchase of Redeemable Preferred Stock		0	0
Payments for Repurchase of Common Stock	0	0	0
Payments of Dividends	0	0	0
Dividends paid and returns of contributed capital, Intercompany	8,919	4,658	3,617
Capital contributions from parent	(1,217)	(3,908)	(797)
Net cash (used in) provided by financing activities	10,824	2,009	4,037
Effect of exchange-rate changes on cash and cash equivalents	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	(1,432)	449	(235)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(1,833)	(401)	(850)	$ (615)
Restricted Cash	0	0
Consolidation, Eliminations [Member] | Affiliated Entity [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Payments for (Proceeds from) Investments	298
Payments for (Proceeds from) Loans and Leases	$ (2,285)	$ (810)	$ (1,451)