Equities - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	$ 8,617,530	$ 8,165,028	$ 7,705,640
Other comprehensive income, net of tax	(6,991)	(22,312)	7,437
Reclassifications
Balance	8,819,173	8,617,530	8,165,028
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(4,751)	(51,118)	7,633
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	19,908	10,279	21,804
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(172,478)	(140,335)	(132,444)
Other Comprehensive Income (Loss), before Tax	15,157	(40,839)	29,437
Tax effect	(2,359)	8,280	(9,371)
Other comprehensive income, net of tax	12,798	(32,559)	20,066
Reclassifications		416	(27,957)
Balance	(159,680)	(172,478)	(140,335)
Unrealized Net Gain (Loss) on Available for Sale Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	0	0	21,078
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0	25,534
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	0	8,861	10,041
Other Comprehensive Income (Loss), before Tax	0	0	(4,456)
Tax effect	0	0	1,308
Other comprehensive income, net of tax	0	0	(3,148)
Reclassifications		(8,861)	1,968
Balance	0	0	8,861
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	16,430	37,709	1,031
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(22,291)	(9,843)	1,704
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	15,297	(5,882)	(6,954)
Other Comprehensive Income (Loss), before Tax	(5,861)	27,866	2,735
Tax effect	1,450	(7,670)	(195)
Other comprehensive income, net of tax	(4,411)	20,196	2,540
Reclassifications		983	(1,468)
Balance	10,886	15,297	(5,882)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(17,021)	(9,990)	(10,062)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0	(2,042)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(69,752)	(62,559)	(51,003)
Other Comprehensive Income (Loss), before Tax	(17,021)	(9,990)	(12,104)
Tax effect	1,643	41	83
Other comprehensive income, net of tax	(15,378)	(9,949)	(12,021)
Reclassifications		2,756	465
Balance	(85,130)	(69,752)	(62,559)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(5,342)	(23,399)	19,680
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(2,383)	436	(4,068)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(226,933)	(199,915)	(180,360)
Other Comprehensive Income (Loss), before Tax	(7,725)	(22,963)	15,612
Tax effect	734	651	(8,175)
Other comprehensive income, net of tax	(6,991)	(22,312)	7,437
Reclassifications	0	(4,706)	(26,992)
Balance	$ (233,924)	$ (226,933)	$ (199,915)