Long-Term Incentive Employee Compensation Outstanding RSUs, Cash Settled RSUs and PSUs (Detail) - shares shares in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity-settled RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity and Cash settled shares	0.4	0.5	0.7
Cash-settled RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity and Cash settled shares	0.0	0.1	0.1
Equity-settled PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity and Cash settled shares	0.4	0.4	0.4