Equities - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	$ 8,165,028	$ 7,705,640	$ 7,759,159
Other comprehensive income (loss), net of tax	(22,312)	7,437	31,170
Reclassification of tax effects to capital reserves	0
Balance	8,617,530	8,165,028	7,705,640
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(51,118)	7,633	25,216
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	10,279	21,804	26,174
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(140,335)	(132,444)	(165,146)
Total other comprehensive income (loss), before tax	(40,839)	29,437	51,390
Tax effect	8,280	(9,371)	(18,688)
Other comprehensive income (loss), net of tax	(32,559)	20,066	32,702
Reclassification of tax effects to capital reserves	416	(27,957)
Balance	(172,478)	(140,335)	(132,444)
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	21,078	7,117
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	(25,534)	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	8,861	10,041	5,656
Total other comprehensive income (loss), before tax	0	(4,456)	7,117
Tax effect	0	1,308	(2,732)
Other comprehensive income (loss), net of tax	0	(3,148)	4,385
Reclassification of tax effects to capital reserves	(8,861)	1,968
Balance	0	8,861	10,041
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	37,709	1,031	1,892
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(9,843)	1,704	1,742
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(5,882)	(6,954)	(9,196)
Total other comprehensive income (loss), before tax	27,866	2,735	3,634
Tax effect	(7,670)	(195)	(1,392)
Other comprehensive income (loss), net of tax	20,196	2,540	2,242
Reclassification of tax effects to capital reserves	983	(1,468)
Balance	15,297	(5,882)	(6,954)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(9,990)	(10,062)	(7,960)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	(2,042)	15
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(62,559)	(51,003)	(42,844)
Total other comprehensive income (loss), before tax	(9,990)	(12,104)	(7,945)
Tax effect	41	83	(214)
Other comprehensive income (loss), net of tax	(9,949)	(12,021)	(8,159)
Reclassification of tax effects to capital reserves	2,756	465
Balance	(69,752)	(62,559)	(51,003)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(23,399)	19,680	26,265
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	436	(4,068)	27,931
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(199,915)	(180,360)	(211,530)
Total other comprehensive income (loss), before tax	(22,963)	15,612	54,196
Tax effect	651	(8,175)	(23,026)
Other comprehensive income (loss), net of tax	(22,312)	7,437	31,170
Reclassification of tax effects to capital reserves	(4,706)	(26,992)
Balance	$ (226,933)	$ (199,915)	$ (180,360)