Commitments and Contingencies (Narrative) (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Jul. 01, 2021	Dec. 31, 2020	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%
Additions (reductions) in depots balance	10,000,000,000
SEC investigation liability and non-deductible charge	200,000,000
Performance Guarantee [Member]
Loss Contingencies [Line Items]
Liability for guarantees	0
Ending IDA balance	142,000,000,000.0		$ 154,100,000,000
Margin Requirements [Member]
Loss Contingencies [Line Items]
Funds drawn under LOC's	$ 0