Derivatives - Interest Rate Swap Contracts, Swaptions and Futures Contracts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional Amount	$ 7,210,000,000	$ 5,337,000,000
Weighted Average Remaining Term (Months)	77 months	58 months
Weighted Average Rate	0.63%	0.24%
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Derivative [Line Items]
Notional Amount	$ 1,203,000,000	$ 2,230,000,000
Fed Funds Effective Rate Overnight Index Swap Rate
Derivative [Line Items]
Notional Amount	6,007,000,000	3,107,000,000
Less than 3 years
Derivative [Line Items]
Notional Amount	$ 1,593,000,000	$ 2,230,000,000
Weighted Average Remaining Term (Months)	15 months	12 months
Weighted Average Rate	0.08%	0.06%
Greater than or equal to 3 years and less than 5 years
Derivative [Line Items]
Notional Amount	$ 708,000,000	$ 463,000,000
Weighted Average Remaining Term (Months)	57 months	45 months
Weighted Average Rate	0.24%	0.14%
Greater than or equal to 5 years and less than 7 years
Derivative [Line Items]
Notional Amount	$ 707,000,000	$ 942,000,000
Weighted Average Remaining Term (Months)	64 months	72 months
Weighted Average Rate	0.88%	0.28%
Greater than 7 years
Derivative [Line Items]
Notional Amount	$ 4,202,000,000	$ 1,702,000,000
Weighted Average Remaining Term (Months)	107 months	113 months
Weighted Average Rate	0.87%	0.50%
Minimum | Greater than or equal to 3 years and less than 5 years
Derivative [Line Items]
Derivative, remaining maturity	3 years	3 years
Minimum | Greater than or equal to 5 years and less than 7 years
Derivative [Line Items]
Derivative, remaining maturity	5 years	5 years
Minimum | Greater than 7 years
Derivative [Line Items]
Derivative, remaining maturity	7 years	7 years
Maximum | Less than 3 years
Derivative [Line Items]
Derivative, remaining maturity	3 years	3 years
Maximum | Greater than or equal to 3 years and less than 5 years
Derivative [Line Items]
Derivative, remaining maturity	5 years	5 years
Maximum | Greater than or equal to 5 years and less than 7 years
Derivative [Line Items]
Derivative, remaining maturity	7 years	7 years