Pension and Other Benefit Plans - Fair Value by Investment Category and Level Within Fair Value Hierarchy (Details) - USD ($) $ in Millions	Mar. 31, 2019	May 31, 2018	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	$ 247	$ 419
Total investments measured at NAV	154
Total investments	401
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	18
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	151
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	78		$ 0
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	12
Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Cash and cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	12
Cash and cash equivalents | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Equity funds
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	122
Total investments measured at NAV	20
Equity funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	18
Equity funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	104
Equity funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	35
Total investments measured at NAV	32
Fixed income | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Fixed income | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	35
Fixed income | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	53
Total investments measured at NAV	102
Real estate funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Real estate funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Real estate funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	53
Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	25
Hedge funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Hedge funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	0
Hedge funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments measured at fair value	$ 25		$ 0