Summary of Cumulative Effect of the Changes Made for the Adoption of ASU 2016-13 (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings	$ 11,005.2		$ 10,398.5
Financial Services
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Finance and other receivables, net	11,820.7	$ 12,079.8	12,086.0
Other assets	681.7	715.1	715.0
Deferred taxes and other liabilities	$ 854.6	788.7	790.2
Retained earnings		10,393.9	$ 10,398.5
Financial Services | ASU 2016-13 | Adjustments
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Finance and other receivables, net		(6.2)
Other assets		0.1
Deferred taxes and other liabilities		(1.5)
Retained earnings		$ (4.6)