Consolidated Balance Sheet - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Cash and cash equivalents	$ 523.6	$ 402.6
Restricted cash	4,266.1	4,063.7
Premiums and fees receivable	18,452.0	11,753.1
Other current assets	1,502.7	1,451.0
Total current assets	24,744.4	17,670.4
Fixed assets - net	569.6	500.8
Deferred income taxes	1,136.8	1,228.5
Other noncurrent assets	949.1	966.5
Right-of-use assets	363.2	358.6
Goodwill	9,036.4	8,666.2
Amortizable intangible assets - net	3,190.9	3,954.0
Total assets	39,990.4	33,345.0
Premiums payable to underwriting enterprises	20,381.2	13,845.6
Accrued compensation and other current liabilities	1,677.0	1,895.1
Deferred revenue - current	559.3	520.9
Premium financing debt	177.2	228.4
Corporate related borrowings - current	710.0	245.0
Total current liabilities	23,504.7	16,735.0
Corporate related borrowings - noncurrent	5,561.5	5,810.2
Deferred revenue - noncurrent	62.9	58.7
Lease liabilities - noncurrent	313.3	309.3
Other noncurrent liabilities	1,686.2	1,871.7
Total liabilities	31,128.6	24,784.9
Stockholders' equity:
Common stock - issued and outstanding 210.3 shares in 2022 and 208.5 shares in 2021	210.3	208.5
Capital in excess of par value	6,267.0	6,143.7
Retained earnings	3,388.7	2,882.3
Accumulated other comprehensive loss	(1,057.3)	(726.1)
Stockholders' equity attributable to controlling interests	8,808.7	8,508.4
Stockholders' equity attributable to noncontrolling interests	53.1	51.7
Total stockholders' equity	8,861.8	8,560.1
Total liabilities and stockholders' equity	$ 39,990.4	$ 33,345.0