v3.26.1
POSTRETIREMENT BENEFIT PLANS - Effect on Operations of Pension Plans (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Principal pension        
Defined Benefit Plan Disclosure [Line Items]        
Service cost – operating $ 6 $ 5 $ 12 $ 11
Interest cost 135 140 270 280
Expected return on plan assets (170) (178) (341) (356)
Amortization of net loss (gain) (54) (50) (109) (100)
Amortization of prior service cost (credit) 2 0 3 0
Curtailment/settlement loss (gain) 0 0 0 0
Non-operating benefit costs (income) (88) (88) (176) (175)
Net periodic expense (income) (82) (82) (165) (164)
Other pension        
Defined Benefit Plan Disclosure [Line Items]        
Service cost – operating 7 7 14 14
Interest cost 55 57 114 111
Expected return on plan assets (80) (80) (167) (155)
Amortization of net loss (gain) 6 10 12 19
Amortization of prior service cost (credit) (2) (2) (4) (4)
Curtailment/settlement loss (gain) 0 0 0 1
Non-operating benefit costs (income) (22) (15) (45) (28)
Net periodic expense (income) (14) (8) (30) (14)
Principal retiree benefit        
Defined Benefit Plan Disclosure [Line Items]        
Service cost – operating 1 1 2 3
Interest cost 8 10 16 20
Expected return on plan assets 0 0 0 0
Amortization of net loss (gain) (13) (10) (26) (19)
Amortization of prior service cost (credit) (14) (14) (28) (27)
Curtailment/settlement loss (gain) 0 0 0 0
Non-operating benefit costs (income) (19) (13) (38) (27)
Net periodic expense (income) $ (18) $ (12) $ (36) $ (24)