Debt - Schedule of Selected Information about Debt Issues (Details) - USD ($)	3 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024
Debt Instrument [Line Items]
Long-term debt, par value, gross	$ 2,350,000,000
Total short-term debt, par value	479,500,000
Total debt, par value	2,829,500,000
Unamortized discount & issuance costs, noncurrent	(25,055,000)
Unamortized discount & issuance costs, current	(2,609,000)
Total debt, unamortized discount & issuance costs,	(27,664,000)
Long-term debt	2,324,945,000	$ 2,324,251,000
Total short-term debt, book value	476,891,000	415,401,000
Total debt, book value	2,801,836,000	2,739,652,000
Fair Value	2,150,340,000
Total short-term debt, fair value	476,891,000
Total debt, fair value	2,627,231,000
FHLB borrowings
Debt Instrument [Line Items]
Total short-term debt, par value	70,000,000		$ 242,000,000
Unamortized discount & issuance costs, current	0
Total short-term debt, book value	70,000,000	0
Total short-term debt, fair value	70,000,000
Commercial paper
Debt Instrument [Line Items]
Total short-term debt, par value	409,500,000
Unamortized discount & issuance costs, current	(2,609,000)
Total short-term debt, book value	406,891,000	415,401,000
Total short-term debt, fair value	$ 406,891,000
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	(2,814,000)
Debt	547,186,000	546,999,000
Long-term debt, gross, fair value	$ 548,751,000
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	(2,750,000)
Debt	397,250,000	397,132,000
Long-term debt, gross, fair value	$ 346,216,000
Senior Notes Due 2032
Debt Instrument [Line Items]
Coupon Rate	4.80%
Long-term debt, par value, gross	$ 250,000,000
Unamortized discount & issuance costs, noncurrent	(3,623,000)
Debt	246,377,000	246,272,000
Long-term debt, gross, fair value	242,348,000
Senior Notes Due 2032 | Consolidation Eliminations | Subsidiaries
Debt Instrument [Line Items]
Long-term debt, net, book value	$ 150,000,000
Senior Notes Due 2034
Debt Instrument [Line Items]
Coupon Rate	5.85%
Long-term debt, par value, gross	$ 450,000,000
Unamortized discount & issuance costs, noncurrent	(5,085,000)
Debt	444,915,000	444,814,000
Long-term debt, gross, fair value	$ 459,194,000
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	(1,552,000)
Debt	123,448,000	123,443,000
Long-term debt, gross, fair value	$ 97,340,000
Basis spread	1.35%
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	(7,592,000)
Debt	317,408,000	317,387,000
Long-term debt, gross, fair value	$ 208,130,000
Term Loan Due 2027
Debt Instrument [Line Items]
Coupon Rate	5.798%
Long-term debt, par value, gross	$ 250,000,000
Unamortized discount & issuance costs, noncurrent	(1,639,000)
Debt	248,361,000	$ 248,204,000
Long-term debt, gross, fair value	$ 248,361,000