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Financing: Short-Term Debt: (Details)		3 Months Ended	12 Months Ended
	Feb. 24, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2022 USD ($) CreditExtension	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 19, 2021 USD ($)
Short-term Debt [Line Items]
Amount outstanding			$ 535,600,000	$ 420,180,000
Commercial Paper, Maximum Borrowing Capacity			750,000,000
Term Loan - borrowings			0	800,000,000	$ 0
Repayments of Other Short-term Debt			$ 0	800,000,000	$ 0
Commercial Paper
Short-term Debt [Line Items]
Debt Instrument, Term			397 days
Line of Credit | Senior Unsecured Notes Due 2021
Short-term Debt [Line Items]
Debt Instrument, Term	9 months
Term Loan - borrowings	$ 800,000,000
Prepayment penalty			$ 0
Repayments of Other Short-term Debt		$ 200,000,000
Revolving Credit Facility
Short-term Debt [Line Items]
Line of Credit Facility, Current Borrowing Capacity						$ 750,000,000
Number Of One-Year Extension Options | CreditExtension			2
Debt Instrument, Term			1 year
Maximum amount outstanding (based on daily outstanding balances)						$ 1,000,000,000.0
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.175%
Debt Issuance Cost, Gross, Noncurrent			$ 8,900,000
Revolving Credit Facility | Base Rate
Short-term Debt [Line Items]
Weighted average interest rates			0.125%
Revolving Credit Facility | Eurodollar
Short-term Debt [Line Items]
Weighted average interest rates			1.125%
Revolving Credit Facility | Letter of Credit
Short-term Debt [Line Items]
Weighted average interest rates			1.125%
Revolving Credit Facility | Commercial Paper
Short-term Debt [Line Items]
Amount outstanding			$ 535,600,000	420,180,000
Letters of credit			24,626,000	27,209,000
Available capacity			189,774,000	302,611,000
Maximum amount outstanding (based on daily outstanding balances)			572,300,000	440,000,000
Average amount outstanding (based on daily outstanding balances)			$ 390,653,000	$ 258,392,000
Weighted average interest rates			2.11%	0.22%
Weighted average interest rates			4.88%	0.30%

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