Financing Agreements (Financing Agreements, at Fair Values Narrative) (Details) - USD ($) $ in Thousands		9 Months Ended
	Jun. 26, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Agreements [Line Items]
Agreement amount		$ 4,864,554		$ 10,044,844
Financial instruments		4,851,121		$ 10,031,606
Senior secured credit agreement
Financing Agreements [Line Items]
Agreement amount		481,250	$ 500,000
Financial instruments		473,993
Financing agreements with mark-to-market collateral provisions
Financing Agreements [Line Items]
Agreement amount		1,489,097
Financial instruments	$ 1,650,000	1,490,271
Financing agreements with non-mark-to-market collateral provisions
Financing Agreements [Line Items]
Agreement amount		1,723,959
Financial instruments		1,727,407
Non Mark to Market Financing Facilities
Financing Agreements [Line Items]
Financial instruments		1,400,000
Debt instrument term	2 years
Debt instrument, term, extension	3 years
Non Mark to Market Financing Facilities on Rehabilitation Loans
Financing Agreements [Line Items]
Long-term debt, term	2 years
Debt outstanding		$ 359,000
Minimum | Financing agreements with mark-to-market collateral provisions
Financing Agreements [Line Items]
Debt instrument term		1 month
Maximum | Financing agreements with mark-to-market collateral provisions
Financing Agreements [Line Items]
Debt instrument term		3 months