Guarantees - Schedule of Long-Term Standby Purchase Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Long-Term Standby Purchase Commitments
Guarantor Obligations [Line Items]
Maximum principal amount	$ 3,002,349	$ 3,163,059
Weighted-average remaining maturity	15 years 2 months 12 days	15 years 3 months 18 days
Guarantee obligations issued after January 1, 2003
Guarantor Obligations [Line Items]
Maximum principal amount	$ 3,500,000	$ 4,000,000
Guarantee obligations issued after January 1, 2003 | Long-Term Standby Purchase Commitments
Guarantor Obligations [Line Items]
Guarantee and commitment obligation	34,470	35,880
Guarantee obligations issued prior to January 1, 2003
Guarantor Obligations [Line Items]
Maximum principal amount	$ 15,500	$ 23,800