Revenue from Contracts with Customers - Contract Liabilities, Capitalized Costs and Receivables (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Revenue disaggregated by segment
Receivables for revenue from contracts with customers	$ 537	$ 537
Financial planning fees | Other liabilities
Revenue disaggregated by segment
Contract liabilities	168	160
Financial planning fees | Other assets
Revenue disaggregated by segment
Capitalized contract costs	135	129
Management and financial advice fees | European-based asset management business of BMO Financial Group
Revenue disaggregated by segment
Capitalized contract costs	$ 25	$ 33