Debt - Schedule of Selected Information about Debt Issues (Details) - USD ($)	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Long-term debt, par value, gross	$ 2,350,000,000
Total short-term debt, par value	443,908,000
Total debt, par value	2,793,908,000
Unamortized discount & issuance costs, noncurrent	(26,324,000)
Unamortized discount & issuance costs, current	(6,490,000)
Total debt, unamortized discount & issuance costs,	(32,814,000)
Long-term debt	2,323,676,000	$ 1,629,559,000
Total short-term debt, book value	437,418,000	486,113,000
Total debt, book value	2,761,094,000	2,115,672,000
Fair Value	2,202,644,000
Total short-term debt, fair value	437,418,000
Total debt, fair value	2,640,062,000
FHLB borrowings
Debt Instrument [Line Items]
Total short-term debt, par value	17,000,000	0
Unamortized discount & issuance costs, current	0
Total short-term debt, book value	17,000,000	0
Total short-term debt, fair value	17,000,000
Commercial paper
Debt Instrument [Line Items]
Total short-term debt, par value	426,908,000
Unamortized discount & issuance costs, current	(6,490,000)
Total short-term debt, book value	420,418,000	316,564,000
Total short-term debt, fair value	420,418,000
Term Loan Due November 11 2024
Debt Instrument [Line Items]
Total short-term debt, par value	0
Unamortized discount & issuance costs, current	0
Total short-term debt, book value	0	169,549,000
Total short-term debt, fair value	$ 0
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	(3,180,000)
Debt	546,820,000	546,283,000
Long-term debt, gross, fair value	$ 550,088,000
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	(2,983,000)
Debt	397,017,000	396,670,000
Long-term debt, gross, fair value	$ 344,796,000
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	(3,828,000)
Debt	246,172,000	245,873,000
Long-term debt, gross, fair value	248,443,000
Senior Notes Due June 15 2032 | Consolidation Eliminations | Subsidiaries
Debt Instrument [Line Items]
Long-term debt, net, book value	$ 150,000,000
5.85% Senior notes due September 15, 2034
Debt Instrument [Line Items]
Coupon Rate	5.85%
Long-term debt, par value, gross	$ 450,000,000
Unamortized discount & issuance costs, noncurrent	(5,188,000)
Debt	444,812,000	0
Long-term debt, gross, fair value	$ 464,881,000
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	(1,561,000)
Debt	123,439,000	123,427,000
Long-term debt, gross, fair value	$ 109,657,000
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	(7,633,000)
Debt	317,367,000	317,306,000
Long-term debt, gross, fair value	$ 236,730,000
Term Loan Due November 11 2024
Debt Instrument [Line Items]
Coupon Rate	6.593%
Long-term debt, par value, gross	$ 250,000,000
Unamortized discount & issuance costs, noncurrent	(1,951,000)
Debt	248,049,000	$ 0
Long-term debt, gross, fair value	$ 248,049,000
Basis spread	1.35%