Financing Agreements (Borrowings Under Repurchase Agreement) (Details) - Repurchase agreements - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Financing agreements	$ 2,494,976,000	$ 9,140,944,000
Weighted Average Interest Rate	3.16%	2.99%
Less debt issuance costs	$ 0	$ 1,123,000
Total financing agreements less debt issuance costs	2,494,976,000	9,139,821,000
Within 30 days
Debt Securities, Available-for-sale [Line Items]
Financing agreements	$ 2,494,976,000	$ 4,472,120,000
Weighted Average Interest Rate	3.16%	2.55%
Over 30 days to 3 months
Debt Securities, Available-for-sale [Line Items]
Financing agreements	$ 0	$ 2,746,384,000
Weighted Average Interest Rate	0.00%	3.43%
Over 3 months to 12 months
Debt Securities, Available-for-sale [Line Items]
Financing agreements	$ 0	$ 1,014,441,000
Weighted Average Interest Rate	0.00%	3.36%
Over 12 months
Debt Securities, Available-for-sale [Line Items]
Financing agreements	$ 0	$ 907,999,000
Weighted Average Interest Rate	0.00%	3.44%

Finance Agreement, Net of Debt Issuance Costs

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- Definition

Financing Agreements, Liabilities

+ References

No definition available.

+ Details

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- Definition

Interest rate on the amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(A)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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