Commitments, contingencies, and guarantees Commitments, Contingencies, And Gaurentees (Letter of Credit Narrative) - USD ($) $ in Billions	Oct. 31, 2017	Oct. 25, 2017	Sep. 30, 2017
Line of Credit Facility [Line Items]
Other Investments Limited Partnerships And Partially Owned Investment Companies Funding Commitments			$ 1.7
Line of Credit Facility, Current Borrowing Capacity			$ 1.5
Subsequent Event [Member]
Line of Credit Facility [Line Items]
Other Investments Limited Partnerships And Partially Owned Investment Companies Funding Commitments	$ 2.5
Line of Credit Facility, Maximum Borrowing Capacity		$ 2.0
Line of Credit Facility, Current Borrowing Capacity		1.0
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases		$ 1.0