Schedule II - Condensed Statements of Cash Flows Parent Company (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Cash provided by operating activities	$ 354.3	$ 777.6	$ 1,219.9
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisitions/dispositions, net of cash acquired/divested	(24.7)	(277.5)	(186.8)
Purchases of equity securities	(170.7)	(157.1)	(198.4)
Cash provided by (used for) investing activities	599.5	(393.0)	(3,393.1)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from issuance of unsecured senior notes	0.0	0.0	641.9
Repayment of senior unsecured notes	(250.0)
Net activity related to noncontrolling interests	(7.1)	(2.2)	(4.3)
Net proceeds in connection with share-based compensation	0.4	2.5	6.3
Repurchases of Company shares	(72.7)	(440.7)	(99.2)
Payments of cash dividends	(216.6)	(217.5)	(213.0)
Cash provided by (used for) financing activities	1,423.1	(376.4)	2,126.1
Net (decrease) increase in cash and cash equivalents	2,381.8	(4.5)	(47.5)
Cash and cash equivalents—Beginning of year	1,223.5	1,228.0	1,275.5
Cash and cash equivalents—End of year	3,605.3	1,223.5	1,228.0
Parent Company
CASH FLOWS FROM OPERATING ACTIVITIES:
Cash provided by operating activities	309.0	778.7	641.4
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisitions/dispositions, net of cash acquired/divested	(2.5)	(296.0)	0.0
Net payments to subsidiaries	(160.8)	(154.6)	(259.5)
Purchases of equity securities	(25.0)	0.0	0.0
Cash provided by (used for) investing activities	(188.3)	(450.6)	(259.5)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from issuance of unsecured senior notes	0.0	0.0	641.9
Repayment of senior unsecured notes	(250.0)	0.0	0.0
Net activity related to noncontrolling interests	0.3	0.0	0.0
Net proceeds in connection with share-based compensation	0.4	2.5	6.3
Repurchases of Company shares	(72.7)	(440.7)	(99.2)
Payments of cash dividends	(216.6)	(217.5)	(213.0)
Cash provided by (used for) financing activities	(538.6)	(655.7)	336.0
Net (decrease) increase in cash and cash equivalents	(417.9)	(327.6)	717.9
Cash and cash equivalents—Beginning of year	597.2	924.8	206.9
Cash and cash equivalents—End of year	$ 179.3	$ 597.2	$ 924.8

The cash outflow to acquire equity securities.

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Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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