Long-Term Incentive Employee Compensation Outstanding RSUs, Cash Settled RSUs and PSUs (Detail) - shares shares in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity settled RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity and Cash settled shares	0.7	0.7	0.7
Cash settled RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity and Cash settled shares	0.1	0.1	0.1
PSU awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity and Cash settled shares	0.4	0.4	0.3