Commitments and Contingencies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Oct. 06, 2020
Loss Contingencies [Line Items]
Aggregate face amount of letter of credit agreements	$ 15,000,000
Reduction in deposit balance over 12 month period			$ 10,000,000,000
Floor amount			$ 50,000,000,000
Percentage of fixed rate investments			80.00%
Balance	154,100,000,000		$ 144,600,000,000
Performance Guarantee [Member]
Loss Contingencies [Line Items]
Liability	0
Margin Requirements [Member]
Loss Contingencies [Line Items]
Funds drawn under LOC's	0
First Mortgage [Member]
Loss Contingencies [Line Items]
Financing receivable, purchased during period	8,700,000,000	$ 4,400,000,000
Home Equity Line of Credit [Member]
Loss Contingencies [Line Items]
Financing receivable, purchased during period	$ 458,000,000	$ 242,000,000