Retirement Plans - Schedule of MTM Adjustments (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
May 31, 2018	May 31, 2017	May 31, 2018	May 31, 2017	May 31, 2016
Actuarial Gain Loss By Component Pre Tax [Abstract]
Discount rate changes			$ (613)	$ 266	$ 1,129
Demographic assumption experience			382	450	(916)
Annuity contract purchase			210
Actual versus expected return on assets			11	(740)	1,285
Total mark-to-market (gain) loss	$ (10)	$ (24)	$ (10)	$ (24)	$ 1,498

Actuarial gain loss by component pre-tax.

No definition available.

Name:	fdx_ActuarialGainLossByComponentPreTaxAbstract
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The amount of actuarial gain/loss attributable to the annuity contract purchase.

No definition available.

Name:	fdx_AnnuityContractPurchase
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Balance Type:	debit
Period Type:	duration

The amount of actuarial gain/loss attributable to the discount rate.

No definition available.

Name:	fdx_GainLossOnDiscountRate
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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

The amount of actuarial gain/loss attributable to demographic assumptions.

No definition available.

Name:	fdx_GainLossOnPreTaxMarkToMarketDemographicAssumptionExperience
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The annual retirement plan amount recorded for actuarial gains and losses calculated using actual fair value of plan assets.

No definition available.

Name:	fdx_RetirementPlansMarketToMarketAdjustment
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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

The amount of actuarial gain/loss attributable to the return on assets.

No definition available.