Retirement Plans - Additional Information (Details)	1 Months Ended		3 Months Ended	12 Months Ended
	May 31, 2018 USD ($) RetireeandBeneficiary	May 31, 2017 USD ($) Employee	Feb. 28, 2018 USD ($)	May 31, 2020 USD ($)	May 31, 2019 USD ($)	May 31, 2018 USD ($)	May 31, 2017 USD ($)	May 31, 2016
Defined Benefit Plan Disclosure [Line Items]
U.S. pension plan actual rate of return on assets					4.05%	6.30%	9.20%
Weighted average discount rate percent all pension postretirement plans					3.69%	4.11%	3.98%	4.04%
Actual rate of return on plan assets for the 15-year period					7.50%
Amounts recognized in other comprehensive income primarily related to amortization of prior service cost, net of tax					$ 92,000,000	$ 89,000,000	$ 75,000,000
Defined benefit plan health care cost trend rate assumed for next fiscal year					6.00%
Defined benefit plan ultimate health care cost trend rate					4.50%
Defined benefit plan year that rate reaches ultimate trend rate					2037
Metropolitan Life Insurance Company [Member]
Defined Benefit Plan Disclosure [Line Items]
One-time settlement loss	$ 210,000,000
U.S. Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions by employer			$ 1,500,000,000		$ 1,000,000,000	$ 2,500,000,000
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on assets					6.75%	6.50%	6.50%
Pension Plans [Member] | U.S. Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on assets					6.75%	6.50%	6.50%
Number of former employees elected to receive lump sum distribution | Employee		18,300
Lump sum amount paid to former employees		$ 1,300,000,000
Group annuity contract and transfer						$ 6,178,000,000
Defined benefit plan contributions by employer					$ 1,034,000,000	2,547,000,000
Amounts recognized in other comprehensive income primarily related to amortization of prior service cost					118,000,000	118,000,000
Amounts recognized in other comprehensive income primarily related to amortization of prior service cost, net of tax					91,000,000	83,000,000
Pension Plans [Member] | U.S. Plans [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions by employer				$ 0
Pension Plans [Member] | U.S. Plans [Member] | Metropolitan Life Insurance Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan responsibility transferred to number of retirees and beneficiaries | RetireeandBeneficiary	41,000
Group annuity contract and transfer	$ 6,000,000,000
Voluntary Contribution [Member] | U.S. Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions by employer					$ 1,000,000,000	$ 2,478,000,000
Voluntary Contribution [Member] | U.S. Plans [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions by employer				$ 1,000,000,000