Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Amortized Cost	$ 8,537.3	$ 8,285.0
Available-for-sale Equity Securities, Amortized Cost Basis	3,089.1	3,039.1
Debt Securities, Held-to-maturity, Fair Value	$ 1,058.2	$ 1,034.5
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	75,000,000	75,000,000
Preferred Stock, Shares Outstanding	0	0
Common Stock, Par or Stated Value Per Share	$ 1.00	$ 1.00
Common Stock, Shares Authorized	500,000,000	500,000,000
Common Stock, Shares, Issued	303,652,553	302,714,502
Common Class B [Member]
Common Stock, Par or Stated Value Per Share	$ 1.00	$ 1.00
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Shares, Issued	0	0