Commitments and Contingencies (Narrative) (Details) - USD ($)	1 Months Ended	7 Months Ended
	Jul. 31, 2021	Jul. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Oct. 06, 2020	Oct. 05, 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%
SEC investigation liability and non-deductible charge			200,000,000
Subsequent Event [Member]
Loss Contingencies [Line Items]
Additions (reductions) in depots balance	$ (8,700,000,000)	$ 9,900,000,000
Performance Guarantee [Member]
Loss Contingencies [Line Items]
Liability for guarantees			0
Ending IDA balance			150,000,000,000.0	$ 154,100,000,000		$ 144,600,000,000
Margin Requirements [Member]
Loss Contingencies [Line Items]
Funds drawn under LOC's			$ 0