Debt - Schedule of Selected Information about Debt Issues (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Long-term debt, par value, gross	$ 1,650,000,000
Total short-term debt, par value	736,000,000
Total debt, par value	2,386,000,000
Unamortized discount & issuance costs, noncurrent	(20,022,000)
Unamortized discount & issuance costs, current	(2,456,000)
Total debt, unamortized discount & issuance costs,	(22,478,000)
Long-term debt (estimated fair value: 2024—$1,510,512; 2023—$1,491,229)	1,629,978,000	$ 1,629,559,000
Total short-term debt, book value	733,544,000	486,113,000
Total debt, book value	2,363,522,000	2,115,672,000
Fair Value	1,510,512,000
Total short-term debt, fair value	733,544,000
Total debt, fair value	2,244,056,000
Federal Home Loan Bank Borrowings
Debt Instrument [Line Items]
Total short-term debt, par value	242,000,000	0
Unamortized discount & issuance costs, current	0
Total short-term debt, book value	242,000,000	0
Total short-term debt, fair value	242,000,000
Commercial paper
Debt Instrument [Line Items]
Total short-term debt, par value	324,000,000
Unamortized discount & issuance costs, current	(2,132,000)
Total short-term debt, book value	321,868,000	316,564,000
Total short-term debt, fair value	$ 321,868,000
Senior Notes Due 2028
Debt Instrument [Line Items]
Coupon Rate	4.55%
Long-term debt, par value, gross	$ 550,000,000
Unamortized discount & issuance costs, noncurrent	(3,538,000)
Debt	546,462,000	546,283,000
Long-term debt, gross, fair value	$ 539,198,000
Senior Notes Due 2030
Debt Instrument [Line Items]
Coupon Rate	2.15%
Long-term debt, par value, gross	$ 400,000,000
Unamortized discount & issuance costs, noncurrent	(3,214,000)
Debt	396,786,000	396,670,000
Long-term debt, gross, fair value	$ 334,816,000
Senior Notes Due June 15 2032
Debt Instrument [Line Items]
Coupon Rate	4.80%
Long-term debt, par value, gross	$ 250,000,000
Unamortized discount & issuance costs, noncurrent	(4,028,000)
Debt	245,972,000	245,873,000
Long-term debt, gross, fair value	242,950,000
Senior Notes Due June 15 2032 | Consolidation Eliminations | Subsidiaries
Debt Instrument [Line Items]
Long-term debt, net, book value	$ 150,000,000
Junior Subordinated Debentures Due 2057
Debt Instrument [Line Items]
Coupon Rate	5.275%
Long-term debt, par value, gross	$ 125,000,000
Unamortized discount & issuance costs, noncurrent	(1,569,000)
Debt	123,431,000	123,427,000
Long-term debt, gross, fair value	$ 123,538,000
Junior Subordinated Debentures Due 2061
Debt Instrument [Line Items]
Coupon Rate	4.25%
Long-term debt, par value, gross	$ 325,000,000
Unamortized discount & issuance costs, noncurrent	(7,673,000)
Debt	317,327,000	317,306,000
Long-term debt, gross, fair value	$ 270,010,000
Term Loan Due November 11 2024
Debt Instrument [Line Items]
Coupon Rate	6.68%
Long-term debt, par value, gross	$ 170,000,000
Unamortized discount & issuance costs, noncurrent	(324,000)
Debt	169,676,000	$ 169,549,000
Long-term debt, gross, fair value	$ 169,676,000
Basis spread	1.35%