Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Partners Capital [Abstract]
Net income	$ 1,408,306	$ 1,315,114	$ 1,079,667
Other comprehensive income (loss), net of tax and reclassification adjustments:
Net unrealized losses on investment securities	(19,766)	(64,406)	(79,114)
Cash flow hedges adjustments	(9,912)	(94)	796
Foreign currency translation adjustment	2,241	(2,614)	(925)
Defined benefit plans liability adjustments	22,288	24,105	8,610
Total other comprehensive loss	(5,149)	(43,009)	(70,633)
Total comprehensive income	$ 1,403,157	$ 1,272,105	$ 1,009,034