Stockholders' equity - ASR - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended				9 Months Ended
	May 27, 2020	Feb. 03, 2020	Jan. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020		Sep. 30, 2019	[2]	Mar. 31, 2020
Stockholders Equity Note
Common stock purchases				$ 185		$ 1,367		$ 503,667	[1]	$ 256,006
Treasury stock
Stockholders Equity Note
Common stock purchases				$ 185		$ 1,367		580,003	[1]	203,336
Capital surplus
Stockholders Equity Note
Common stock purchases								(76,336)	[1]	$ 52,670
Accelerate Share Repurchase
Stockholders Equity Note
Stock repurchase program authorized amount			$ 500,000				$ 250,000					$ 500,000
Accelerated share repurchases price paid per share					$ 53.58
Accelerated share repurchases settlement receipt	$ 500,000
Common Shares Repurchased Accelerated Share Repurchase Agreements					1,165,607
Initial shares received as part of an accelerated share repurchase program		7,055,919	7,055,919				3,500,000
Accelerate Share Repurchase | Treasury stock
Stockholders Equity Note
Common stock purchases			$ 400,000				$ 200,000
Accelerate Share Repurchase | Capital surplus
Stockholders Equity Note
Common stock purchases			$ 100,000				$ 50,000	$ 23,000
Accelerate Share Repurchase | COVID-19
Stockholders Equity Note
Stock Repurchased During Period Shares								11,819,135
Accelerated share repurchases price paid per share								$ 42.3043
Common Shares Repurchased Accelerated Share Repurchase Agreements	4,763,216

[1] During the quarter ended March 31, 2020, the Corporation entered into a $500 million accelerated share repurchase transaction with respect to its common stock, which was accounted for as a treasury stock transaction. The transaction was completed on May 27, 2020. Refer to Note 18 for additional information.

[2] During the quarter ended March 31, 2019, the Corporation entered into a $250 million accelerated share repurchase transaction with respect to its common stock, which was accounted for as a treasury stock transaction. Refer to Note 18 for additional information.