v3.8.0.1
Revenue - Schedule of Estimated Technology and Risk Management Revenue Expected to Be Recognized in Future, Related to Unsatisfied Portion of Performance Obligations (Detail) - Technology And Risk Management Revenue
$ in Millions
 3 Months Ended
Mar. 31, 2018
USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-04-01  
Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items]  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period 9 months
Revenue, Remaining Performance Obligation $ 25
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01  
Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items]  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period 1 year
Revenue, Remaining Performance Obligation $ 24
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01  
Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items]  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period 1 year
Revenue, Remaining Performance Obligation $ 20
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01  
Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items]  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period 1 year
Revenue, Remaining Performance Obligation $ 15
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01  
Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items]  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period
Revenue, Remaining Performance Obligation $ 10
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: (nil)  
Schedule of Investment Advisory Administration Fees and Securities Lending Revenue and Performance Fees by Type [line Items]  
Revenue, Remaining Performance Obligation $ 94