New Accounting Pronouncements - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Item Effected [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Cumulative impact of adopting ASU, net of tax	$ (2,240.7)		$ (2,336.8)
Change in Accounting Principle, Accounting Standards Update, Transition Option Elected [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Accounting Standards Update 2018-14
Item Effected [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Dec. 31, 2020
Accounting Standards Update 2016-13 | Revision of Prior Period Adjustment | Cumulative Effect, Period of Adoption, Adjustment
Item Effected [Line Items]
Cumulative impact of adopting ASU, net of tax		$ 0.3