VIEs (Cash Flow Summary) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
VIEs, Primary Beneficiary | Trusts
Variable Interest Entity [Line Items]
Assets securitized	$ 5,282,901,000	$ 5,498,705,000	$ 15,845,707,000	$ 15,340,428,000
Net proceeds from new securitizations	4,662,211,000	4,475,722,000	11,470,857,000	12,232,777,000
Net proceeds from sale of retained bonds	1,293,000	2,414,000	57,286,000	119,719,000
Cash received for servicing fees	242,245,000	242,801,000	735,533,000	740,760,000
Net distributions from Trusts	1,173,276,000	1,018,301,000	2,730,657,000	2,689,735,000
Total cash received from Trusts	6,079,025,000	5,739,238,000	14,994,333,000	15,782,991,000
VIE, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Sales of receivables securitization	636,301,000	0	1,148,587,000	0
Net proceeds from new securitizations	592,455,000	0	1,052,541,000	0
Cash received for servicing fees	6,598,000	7,859,000	17,856,000	27,467,000
Total cash received from Trusts	$ 599,053,000	$ 7,859,000	$ 1,070,397,000	$ 27,467,000