| Derivative Instruments and Hedging Activities Interest Spread on Interest Rate Swaps and Caps (Details) - USD ($) | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | |
| Derivative Instruments, Gain (Loss) [Line Items] | ||||
| Average Notional Amount | $ 21,137,615,000 | $ 13,932,642,000 | $ 20,840,267,000 | $ 37,837,985,000 | 
| Interest Rate Contract [Member] | ||||
| Derivative Instruments, Gain (Loss) [Line Items] | ||||
| Net interest expense (income) on interest rate swaps and caps | 4,400,000 | 800,000 | 8,500,000 | (68,100,000) | 
| Net Long Position [Member] | Interest Rate Contract [Member] | ||||
| Derivative Instruments, Gain (Loss) [Line Items] | ||||
| Average Notional Amount | $ 15,900,000,000 | $ 7,600,000,000 | $ 14,900,000,000 | $ 32,000,000,000 | 
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- Definition Net interest spread on interest rate swap and cap agreements, at fair value. No definition available. 
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