Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional	$ 60,549,307,000	$ 48,445,497,000	$ 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)