Note 7 - Redeemable Noncontrolling Interests (Details Textual) - USD ($) $ in Millions				3 Months Ended		9 Months Ended
	Apr. 14, 2020	Jul. 29, 2019	Jun. 22, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Temporary Equity, Increase from Sale of Parent Equity Interest					$ 64		$ 64
Ashwoods [Member] | Hydro-Québec [Member]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	45.00%
Temporary Equity, Increase from Sale of Parent Equity Interest	$ 7
TM4 Inc. [Member]
Temporary Equity, Stock Issued During Period, Value, New Issues			$ 102
TM4 Inc. [Member] | Hydro-Québec [Member]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners			45.00%
S.M.E. S.p.A. [Member] | Hydro-Québec [Member]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		45.00%
Prestolite E-Propulsion Systems (Beijing) Limited [Member] | Hydro-Québec [Member]
Minority Interest, Ownership Percentage by Noncontrolling Owners, Increase		22.50%
SME and PEPS [Member]
Temporary Equity, Increase from Sale of Parent Equity Interest		$ 64