Net income per common share - Additional Information (Details) - Accelerate Share Repurchase - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	May 27, 2020	Jan. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Jun. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Initial shares received as part of an accelerated share repurchase program		7,055,919	7,055,919		3,500,000
Accelerated share repurchases settlement receipt		$ 500	$ 500		$ 250	$ 500
Common Shares Repurchased Accelerated Share Repurchase Agreements			4,763,216	1,165,607
COVID-19
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common Shares Repurchased Accelerated Share Repurchase Agreements	4,763,216