POSTRETIREMENT BENEFIT PLANS - Composition of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Jan. 01, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		$ 18,908
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		$ 18,908
Pension Plans | Principal Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 14,700		$ 0
Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	14,700
Pension Plans | Other Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	4,518		382
Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	4,518		425
Level 1 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	1,820
Level 1 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	290		60
Level 2 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	6,318
Level 2 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,205		157
Level 3 | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	626		61
Level 3 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	595
Level 3 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	31		61
Net Asset Value | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	5,967
Net Asset Value | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	1,992		147
Global equity securities | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,609
Global equity securities | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	467		67
Global equity securities | Level 1 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	954
Global equity securities | Level 1 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	51		33
Global equity securities | Level 2 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0
Global equity securities | Level 2 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	1		0
Global equity securities | Level 3 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0
Global equity securities | Level 3 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0		0
Global equity securities | Net Asset Value | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	1,655
Global equity securities | Net Asset Value | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	415		34
Debt securities (including cash and cash equivalents) | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	8,121
Debt securities (including cash and cash equivalents) | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,977		205
Debt securities (including cash and cash equivalents) | Level 1 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	866
Debt securities (including cash and cash equivalents) | Level 1 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	239		24
Debt securities (including cash and cash equivalents) | Level 2 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	6,309
Debt securities (including cash and cash equivalents) | Level 2 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,203		150
Debt securities (including cash and cash equivalents) | Level 3 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0
Debt securities (including cash and cash equivalents) | Level 3 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0		0
Debt securities (including cash and cash equivalents) | Net Asset Value | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	946
Debt securities (including cash and cash equivalents) | Net Asset Value | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	535		31
Real estate | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	912
Real estate | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	508		25
Real estate | Level 1 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0
Real estate | Level 1 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0		0
Real estate | Level 2 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0
Real estate | Level 2 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0		0
Real estate | Level 3 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	382
Real estate | Level 3 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	20		12
Real estate | Net Asset Value | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	530
Real estate | Net Asset Value | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	488		13
Private equities and other investments | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	3,058
Private equities and other investments | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	566		128
Private equities and other investments | Level 1 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0
Private equities and other investments | Level 1 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0		3
Private equities and other investments | Level 2 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	9
Private equities and other investments | Level 2 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	1		7
Private equities and other investments | Level 3 | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	213
Private equities and other investments | Level 3 | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	11		49
Private equities and other investments | Net Asset Value | Pension Plans | Principal Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,836
Private equities and other investments | Net Asset Value | Pension Plans | Other Pension Plans | Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 554		$ 69