Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional	$ 8,076,933,000	$ 60,549,307,000	$ 48,445,497,000	$ 55,549,424,000	$ 58,777,783,000	$ 36,528,169,000
Markit IOS Total Return Swap [Member]
Derivative [Line Items]
Notional			41,890,000
Fair Value			(29,000)
Cost Basis			(59,000)
Derivative, Unrealized Gains (Losses)			30,000
Markit IOS Total Return Swap [Member] | Maturity Date, 1/12/2043 [Member]
Derivative [Line Items]
Notional			18,625,000
Fair Value			5,000
Cost Basis			(30,000)
Derivative, Unrealized Gains (Losses)			35,000
Markit IOS Total Return Swap [Member] | Maturity Date, 1/12/2044 [Member]
Derivative [Line Items]
Notional			23,265,000
Fair Value			(34,000)
Cost Basis			(29,000)
Derivative, Unrealized Gains (Losses)			$ (5,000)