Revenue - Summary of Investment Advisory, Administration Fees and Securities Lending Revenue by Client Type and Investment Style (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Total revenue	$ 3,524	$ 3,605	$ 6,870	$ 7,188
Revenue by Client Type [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	2,903	2,944	5,708	5,891
Revenue by Client Type [Member] \| Retail [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	846	858	1,672	1,713
Revenue by Client Type [Member] \| iShares ETFs [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1,128	1,143	2,219	2,301
Revenue by Client Type [Member] \| Institutional Active [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	537	511	1,037	1,038
Revenue by Client Type [Member] \| Institutional Index [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	245	275	492	531
Revenue by Client Type [Member] \| Institutional [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	782	786	1,529	1,569
Revenue by Client Type [Member] \| Cash Management [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	147	157	288	308
Revenue by Client Type [Member] \| Long-term [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	2,756	2,787	5,420	5,583
Revenue by Investment Style [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	2,903	2,944	5,708	5,891
Revenue by Investment Style [Member] \| Active [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1,365	1,352	2,672	2,717
Revenue by Investment Style [Member] \| Index and iShares ETFs [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1,391	1,435	2,748	2,866
Revenue by Investment Style [Member] \| Cash Management [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	147	157	288	308
Revenue by Investment Style [Member] \| Long-term [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 2,756	$ 2,787	$ 5,420	$ 5,583