Equities Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015	Aug. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 7,905,825	$ 7,866,250	$ 7,669,411	$ 6,466,844
Other comprehensive income (loss), net of tax	28,056	2,481	(57,450)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(135,046)	(165,146)	(171,729)	(151,852)
Amounts before reclassifications	25,216	(10,512)	(54,284)
Amounts reclassified out	23,572	20,998	21,681
Total other comprehensive income (loss), before tax	48,788	10,486	(32,603)
Tax effect	(18,688)	(3,903)	12,726
Other comprehensive income (loss), net of tax	30,100	6,583	(19,877)
Unrealized Net Gain (Loss) on Available for Sale Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	10,041	5,656	4,156	4,398
Amounts before reclassifications	7,117	2,447	(396)
Amounts reclassified out	0	0	0
Total other comprehensive income (loss), before tax	7,117	2,447	(396)
Tax effect	(2,732)	(947)	154
Other comprehensive income (loss), net of tax	4,385	1,500	(242)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(6,954)	(9,196)	(5,324)	(2,722)
Amounts before reclassifications	1,892	(11,353)	(5,001)
Amounts reclassified out	1,742	5,071	792
Total other comprehensive income (loss), before tax	3,634	(6,282)	(4,209)
Tax effect	(1,392)	2,410	1,607
Other comprehensive income (loss), net of tax	2,242	(3,872)	(2,602)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(51,711)	(43,040)	(41,310)	(6,581)
Amounts before reclassifications	(8,472)	(1,036)	(30,672)
Amounts reclassified out	15	469	0
Total other comprehensive income (loss), before tax	(8,457)	(567)	(30,672)
Tax effect	(214)	(1,163)	(4,057)
Other comprehensive income (loss), net of tax	(8,671)	(1,730)	(34,729)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(183,670)	(211,726)	(214,207)	$ (156,757)
Amounts before reclassifications	25,753	(20,454)	(90,353)
Amounts reclassified out	25,329	26,538	22,473
Total other comprehensive income (loss), before tax	51,082	6,084	(67,880)
Tax effect	(23,026)	(3,603)	10,430
Other comprehensive income (loss), net of tax	$ 28,056	$ 2,481	$ (57,450)