POSTRETIREMENT BENEFIT PLANS - Funding (Details) $ in Millions	Dec. 31, 2023 USD ($)
Principal pension
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions	$ 235
Principal pension | Power and renewable energy
Defined Benefit Plan Disclosure [Line Items]
Funded percentage, ERISA	87.00%
Funded percentage	93.00%
Principal pension | Aerospace
Defined Benefit Plan Disclosure [Line Items]
Funded percentage, ERISA	93.00%
Funded percentage	90.00%
Other pension
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions	$ 100
Principal retiree benefit
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions	$ 210