v3.26.3
POSTRETIREMENT BENEFIT PLANS - Effect on Operations of Pension Plans (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Principal pension        
Defined Benefit Plan Disclosure [Line Items]        
Service cost – operating $ 6 $ 6 $ 18 $ 17
Interest cost 135 140 405 420
Expected return on plan assets (170) (178) (511) (535)
Amortization of net loss (gain) (54) (50) (163) (149)
Amortization of prior service cost (credit) 2 0 5 0
Curtailment/settlement loss (gain) 0 0 0 0
Non-operating benefit costs (income) (88) (88) (265) (263)
Net periodic expense (income) (82) (82) (247) (246)
Other pension        
Defined Benefit Plan Disclosure [Line Items]        
Service cost – operating 7 7 21 21
Interest cost 61 58 175 169
Expected return on plan assets (89) (82) (256) (237)
Amortization of net loss (gain) 7 10 19 30
Amortization of prior service cost (credit) (2) (2) (6) (6)
Curtailment/settlement loss (gain) 0 0 0 1
Non-operating benefit costs (income) (24) (16) (68) (44)
Net periodic expense (income) (17) (8) (47) (22)
Principal retiree benefit        
Defined Benefit Plan Disclosure [Line Items]        
Service cost – operating 1 1 2 4
Interest cost 8 10 24 29
Expected return on plan assets 0 0 0 0
Amortization of net loss (gain) (13) (10) (39) (29)
Amortization of prior service cost (credit) (14) (14) (42) (41)
Curtailment/settlement loss (gain) (84) (1) (84) (1)
Non-operating benefit costs (income) (103) (14) (140) (41)
Net periodic expense (income) $ (102) $ (13) $ (138) $ (37)