Guarantees - Schedule of Long-Term Standby Purchase Commitments (Details) - LTSPCs - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Maximum principal amount	$ 2,900,166	$ 3,002,349
Weighted-average remaining maturity	15 years 2 months 12 days	15 years 2 months 12 days
Guarantee obligations issued after January 1, 2003
Guarantor Obligations [Line Items]
Guarantee and commitment obligation	$ 33,273	$ 34,470