Parent and Guarantor Condensed Consolidating Financial Statements (Statement of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities			$ 2,009	$ 2,070
Purchases of Equity Securities			(500)	(363)
Proceeds from Sales of Equity Securities			535	484
Payments to Acquire Available-for-sale Securities			(4,094)	(5,490)
Proceeds from Sale of Available-for-sale Securities			390	1,678
Proceeds from maturities and repayment of available-for-sale securities			1,621	1,230
Payments to Acquire Held-to-maturity Securities			(316)	(313)
Proceeds from Sale and Maturity of Held-to-maturity Securities			72	17
Payments to Acquire Finance Receivables			(2,611)	(1,817)
Proceeds from Sale of Loans Held-for-investment			0	1,280
Originations and repayments of loans held-for-investment and other			(638)	(1,588)
Gain (Loss) on Sales of Loans, Net	$ 1	$ 36	2	50
Purchases Of Operating Lease Assets			(2,107)	(1,965)
Disposals of Operating Lease Assets			1,763	3,043
Proceeds from Contributions from Parent			0	0
Returns Of Contributed Capital			0	0
Increase (Decrease) in Non marketable equity securities			(46)	107
Payments for (Proceeds from) Other Investing Activities			(186)	(90)
Net Cash Provided by (Used in) Investing Activities			(6,117)	(3,787)
Proceeds from (Repayments of) Short-term Debt			(4,305)	(1,962)
Increase (Decrease) in Deposit Assets			5,441	7,133
Proceeds from Issuance of Long-term Debt			12,940	9,330
Repayments of Long-term Debt			(9,800)	(14,366)
Payments for Repurchase of Common Stock			(380)	(373)
Payments of Dividends			(115)	(75)
Capital contributions from parent			0	0
Net Cash Provided by (Used in) Financing Activities			3,781	(313)
Effect of Exchange Rate on Cash and Cash Equivalents			(3)	2
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			(330)	(2,028)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	4,939	5,853	4,939	5,853	$ 5,269	$ 7,881
Cash and Cash Equivalents, at Carrying Value	3,924	4,377	3,924	4,377	4,252
Restricted Cash	1,015	1,476	1,015	1,476
Parent Company [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities			958	561
Purchases of Equity Securities			0	0
Proceeds from Sales of Equity Securities			0	0
Payments to Acquire Available-for-sale Securities			0	0
Proceeds from Sale of Available-for-sale Securities			0	0
Proceeds from maturities and repayment of available-for-sale securities			0	0
Payments to Acquire Held-to-maturity Securities			0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities			0	0
Payments to Acquire Finance Receivables			0	(35)
Proceeds from Sale of Loans Held-for-investment			820	67
Originations and repayments of loans held-for-investment and other			1,331	1,044
Gain (Loss) on Sales of Loans, Net	0	32	28	30
Purchases Of Operating Lease Assets			0	0
Disposals of Operating Lease Assets			6	4
Proceeds from Contributions from Parent			(57)	(824)
Returns Of Contributed Capital			194	838
Increase (Decrease) in Non marketable equity securities			0	0
Payments for (Proceeds from) Other Investing Activities			(3)	(21)
Net Cash Provided by (Used in) Investing Activities			2,374	2,938
Proceeds from (Repayments of) Short-term Debt			(505)	1,083
Increase (Decrease) in Deposit Assets			(6)	(123)
Proceeds from Issuance of Long-term Debt			32	353
Repayments of Long-term Debt			(2,412)	(3,323)
Payments for Repurchase of Common Stock			(380)	(373)
Payments of Dividends			(115)	(75)
Capital contributions from parent			0	0
Net Cash Provided by (Used in) Financing Activities			(3,524)	(2,828)
Effect of Exchange Rate on Cash and Cash Equivalents			0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			(192)	671
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1,203	1,660	1,203	1,660	1,395	989
Cash and Cash Equivalents, at Carrying Value	1,071	1,441	1,071	1,441	1,217
Restricted Cash	132	219	132	219
Guarantor Subsidiaries [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities			1,500	0
Purchases of Equity Securities			0	0
Proceeds from Sales of Equity Securities			0	0
Payments to Acquire Available-for-sale Securities			0	0
Proceeds from Sale of Available-for-sale Securities			0	0
Proceeds from maturities and repayment of available-for-sale securities			0	0
Payments to Acquire Held-to-maturity Securities			0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities			0	0
Payments to Acquire Finance Receivables			0	0
Proceeds from Sale of Loans Held-for-investment			0	0
Originations and repayments of loans held-for-investment and other			0	0
Gain (Loss) on Sales of Loans, Net	0	0	0	0
Purchases Of Operating Lease Assets			0	0
Disposals of Operating Lease Assets			0	0
Proceeds from Contributions from Parent			(6)	0
Returns Of Contributed Capital			0	0
Increase (Decrease) in Non marketable equity securities			0	0
Payments for (Proceeds from) Other Investing Activities			0	0
Net Cash Provided by (Used in) Investing Activities			(6)	0
Proceeds from (Repayments of) Short-term Debt			0	0
Increase (Decrease) in Deposit Assets			0	0
Proceeds from Issuance of Long-term Debt			0	0
Repayments of Long-term Debt			0	0
Payments for Repurchase of Common Stock			0	0
Payments of Dividends			0	0
Capital contributions from parent			6	0
Net Cash Provided by (Used in) Financing Activities			(1,494)	0
Effect of Exchange Rate on Cash and Cash Equivalents			0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0	0	0	0	0
Cash and Cash Equivalents, at Carrying Value	0	0	0	0	0
Restricted Cash	0	0	0	0
Non-Guarantor Subsidiaries [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities			2,853	1,856
Purchases of Equity Securities			(500)	(363)
Proceeds from Sales of Equity Securities			535	484
Payments to Acquire Available-for-sale Securities			(4,094)	(5,490)
Proceeds from Sale of Available-for-sale Securities			390	1,678
Proceeds from maturities and repayment of available-for-sale securities			1,621	1,230
Payments to Acquire Held-to-maturity Securities			(316)	(313)
Proceeds from Sale and Maturity of Held-to-maturity Securities			72	17
Payments to Acquire Finance Receivables			(3,431)	(1,782)
Proceeds from Sale of Loans Held-for-investment			0	1,213
Originations and repayments of loans held-for-investment and other			(1,969)	(676)
Gain (Loss) on Sales of Loans, Net	1	4	2	20
Purchases Of Operating Lease Assets			(2,107)	(1,965)
Disposals of Operating Lease Assets			1,757	3,039
Proceeds from Contributions from Parent			0	0
Returns Of Contributed Capital			0	0
Increase (Decrease) in Non marketable equity securities			(46)	107
Payments for (Proceeds from) Other Investing Activities			(183)	27
Net Cash Provided by (Used in) Investing Activities			(8,259)	(2,279)
Proceeds from (Repayments of) Short-term Debt			(3,800)	(3,045)
Increase (Decrease) in Deposit Assets			5,324	7,256
Proceeds from Issuance of Long-term Debt			12,908	7,016
Repayments of Long-term Debt			(7,388)	(11,043)
Payments for Repurchase of Common Stock			0	0
Payments of Dividends			0	0
Capital contributions from parent			57	824
Net Cash Provided by (Used in) Financing Activities			5,023	(2,122)
Effect of Exchange Rate on Cash and Cash Equivalents			(3)	2
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			(386)	(2,543)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	5,321	4,750	5,321	4,750	5,707	7,293
Cash and Cash Equivalents, at Carrying Value	4,438	3,493	4,438	3,493	4,868
Restricted Cash	883	1,257	883	1,257
Consolidation, Eliminations [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Net Cash Provided by (Used in) Operating Activities			(3,302)	(347)
Purchases of Equity Securities			0	0
Proceeds from Sales of Equity Securities			0	0
Payments to Acquire Available-for-sale Securities			0	0
Proceeds from Sale of Available-for-sale Securities			0	0
Proceeds from maturities and repayment of available-for-sale securities			0	0
Payments to Acquire Held-to-maturity Securities			0	0
Proceeds from Sale and Maturity of Held-to-maturity Securities			0	0
Payments to Acquire Finance Receivables			820	0
Proceeds from Sale of Loans Held-for-investment			(820)	0
Originations and repayments of loans held-for-investment and other			0	(1,956)
Gain (Loss) on Sales of Loans, Net	0	0	(28)	0
Purchases Of Operating Lease Assets			0	0
Disposals of Operating Lease Assets			0	0
Proceeds from Contributions from Parent			63	824
Returns Of Contributed Capital			(194)	(838)
Increase (Decrease) in Non marketable equity securities			0	0
Payments for (Proceeds from) Other Investing Activities			0	(96)
Net Cash Provided by (Used in) Investing Activities			(226)	(4,446)
Proceeds from (Repayments of) Short-term Debt			0	0
Increase (Decrease) in Deposit Assets			123	0
Proceeds from Issuance of Long-term Debt			0	1,961
Repayments of Long-term Debt			0	0
Payments for Repurchase of Common Stock			0	0
Payments of Dividends			0	0
Capital contributions from parent			(63)	(824)
Net Cash Provided by (Used in) Financing Activities			3,776	4,637
Effect of Exchange Rate on Cash and Cash Equivalents			0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			248	(156)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(1,585)	(557)	(1,585)	(557)	(1,833)	$ (401)
Cash and Cash Equivalents, at Carrying Value	(1,585)	(557)	(1,585)	(557)	$ (1,833)
Restricted Cash	$ 0	$ 0	0	0
Affiliated Entity [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments			0	0
Gain (Loss) on Sales of Loans, Net			0	0
Net Change in Debt, Intercompany			0	0
Dividends paid and returns of contributed capital, Intercompany			0	0
Affiliated Entity [Member] | Parent Company [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments			0	1
Gain (Loss) on Sales of Loans, Net			83	1,864
Net Change in Debt, Intercompany			(138)	(370)
Dividends paid and returns of contributed capital, Intercompany			0	0
Affiliated Entity [Member] | Guarantor Subsidiaries [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments			0	0
Gain (Loss) on Sales of Loans, Net			0	0
Net Change in Debt, Intercompany			0	0
Dividends paid and returns of contributed capital, Intercompany			(1,500)	0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments			17	269
Gain (Loss) on Sales of Loans, Net			(5)	246
Net Change in Debt, Intercompany			(83)	(1,864)
Dividends paid and returns of contributed capital, Intercompany			(1,995)	(1,266)
Affiliated Entity [Member] | Consolidation, Eliminations [Member]
Parent and Guarantor Consolidating Statement of Cash Flows [Line Items]
Payments for (Proceeds from) Investments			(17)	(270)
Gain (Loss) on Sales of Loans, Net			(78)	(2,110)
Net Change in Debt, Intercompany			221	2,234
Dividends paid and returns of contributed capital, Intercompany			$ 3,495	$ 1,266