Schedule II. Condensed Financial Information of Registrant - Condensed Statement of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Condensed Financial Statements, Captions [Line Items]
Net income	$ 1,161,238	$ 1,070,762	$ 970,755
Other, net	(620)	(17,582)	(24,799)
Cash provided from (used for) operating activities	1,396,391	1,402,440	1,482,425
Cash provided from (used for) investing activities:
Net decrease (increase) in short-term investments	(229,676)	(3,295)	32,381
Loaned money to affiliates	(142,484)	(71,045)	(49,553)
Cash provided from (used for) investing activities	(643,618)	(641,516)	(926,149)
Cash provided from (used for) financing activities:
Repayment of debt	0	0	(165,612)
Payment for debt issuance costs	(6,399)	(7,253)	(757)
Proceeds from commercial paper with original maturities greater than 90 days	487,610	484,726	0
Repayment of commercial paper with original maturities greater than 90 days	(700,993)	(372,011)	0
Issuance of stock	164,448	51,786	114,080
Acquisitions of treasury stock	(880,983)	(1,002,109)	(511,100)
Payment of dividends	(86,067)	(85,485)	(84,116)
Cash provided from (used for) financing activities	(768,052)	(715,835)	(541,487)
Net increase (decrease) in cash	(20,621)	62,169	10,597
Cash at end of year	144,704	165,325	103,156
Cash at beginning of year	165,325	103,156	92,559
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net income	1,161,238	1,070,762	970,755
Equity in earnings of subsidiaries	(1,272,741)	(1,155,705)	(1,024,323)
Cash dividends from subsidiaries	815,741	692,690	459,535
Other, net	79,549	55,243	33,846
Cash provided from (used for) operating activities	783,787	662,990	439,813
Cash provided from (used for) investing activities:
Net decrease (increase) in short-term investments	999	(28,000)	13,996
Investment in subsidiaries	(66,300)	(12)	0
Acquisition of investments	0	(2,850)	(3,950)
Disposition of investments	0	1	0
Loaned money to affiliates	(365,382)	(557,016)	(479,629)
Repayments from affiliates	614,960	394,925	505,929
Additions to properties	(353)	(19,147)	(7,400)
Cash provided from (used for) investing activities	183,924	(212,099)	28,946
Cash provided from (used for) financing activities:
Repayment of debt	0	0	(165,612)
Proceeds from issuance of debt	0	530,000	170,000
Payment for debt issuance costs	(6,399)	(7,253)	(757)
Net change in commercial paper held less than 90 days	102,638	(13,878)	32,961
Proceeds from commercial paper with original maturities greater than 90 days	487,610	484,726	0
Repayment of commercial paper with original maturities greater than 90 days	(700,993)	(372,011)	0
Issuance of stock	164,448	51,756	114,080
Acquisitions of treasury stock	(880,983)	(1,002,109)	(511,100)
Borrowed money from affiliate	312,000	349,000	290,500
Repayments to affiliates	(340,600)	(296,600)	(290,500)
Payment of dividends	(109,337)	(108,755)	(107,386)
Cash provided from (used for) financing activities	(971,616)	(385,124)	(467,814)
Net increase (decrease) in cash	(3,905)	65,767	945
Cash at end of year	62,865	66,770	1,003
Cash at beginning of year	$ 66,770	$ 1,003	$ 58