Shareholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ (9,550)
Other comprehensive (loss)/income before reclassifications	(646)	$ 1,426	$ 4,248
Amounts reclassified from AOCI	(109)	683	1,226
Net current period Other comprehensive (loss)/income	(755)	2,109	5,474
Ending balance	(10,305)	(9,550)
Other comprehensive income (loss), defined benefit plan, gain (loss) arising during period, after tax	(722)	1,533	4,262
Net actuarial gain/(loss) arising during the period, tax	13	(22)	(32)
Other comprehensive income (loss), defined benefit plan, gain (loss), reclassification adjustment from AOCI, after tax	(2)	791	1,155
Amortization of actuarial loss included in net periodic pension cost, tax	0	(11)	(8)
Gain (loss) on discontinuation of cash flow hedge due to forecasted transaction probable of not occurring, net	39
Loss on discontinuation of cash flow hedge due to forecasted transaction Probable of not occurring, tax	(11)
Currency Translation Adjustments
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(167)	(105)	(30)
Other comprehensive (loss)/income before reclassifications	33	(62)	(75)
Net current period Other comprehensive (loss)/income	33	(62)	(75)
Ending balance	(134)	(167)	(105)
Unrealized Gains and Losses on Certain Investments
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		1	1
Other comprehensive (loss)/income before reclassifications	2	(1)
Net current period Other comprehensive (loss)/income	2	(1)
Ending balance	2		1
Unrealized Gains and Losses on Derivative Instruments
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(24)	6	(43)
Other comprehensive (loss)/income before reclassifications	41	(40)	55
Amounts reclassified from AOCI	(5)	10	(6)
Net current period Other comprehensive (loss)/income	36	(30)	49
Ending balance	12	(24)	6
Defined Benefit Pension Plans & Other Postretirement Benefits
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(9,359)	(11,561)	(17,061)
Other comprehensive (loss)/income before reclassifications	(722)	1,529	4,268
Amounts reclassified from AOCI	(104)	673	1,232
Net current period Other comprehensive (loss)/income	(826)	2,202	5,500
Ending balance	(10,185)	(9,359)	(11,561)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(9,550)	(11,659)	(17,133)
Ending balance	$ (10,305)	$ (9,550)	$ (11,659)