Retirement Benefits - Schedule of Amounts Recognized in Other Comprehensive Income (Loss) Related to Postretirement Benefit Plans, Net of Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	$ 103	$ 342	$ (684)
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(4)	(2)	(5)
Incurred but Not Yet Recognized in FAS Expense	99	340	(689)
Actuarial gains and (losses) - Recognition of Previously Deferred Amounts	(595)	(188)	(116)
Net prior service credit and (cost) - Recognition of Previously Deferred Amounts	(39)	112	265
Recognition of Previously Deferred Amounts	(634)	(76)	149
Qualified defined benefit pension plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	99	211	(698)
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(4)	(2)	(5)
Actuarial gains and (losses) - Recognition of Previously Deferred Amounts	(623)	(204)	(133)
Net prior service credit and (cost) - Recognition of Previously Deferred Amounts	(39)	116	274
Retiree medical and life insurance plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	45	108	47
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	0	0	(1)
Actuarial gains and (losses) - Recognition of Previously Deferred Amounts	39	28	25
Net prior service credit and (cost) - Recognition of Previously Deferred Amounts	0	(3)	(8)
Other plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(41)	23	(33)
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	0	0	1
Actuarial gains and (losses) - Recognition of Previously Deferred Amounts	(11)	(12)	(8)
Net prior service credit and (cost) - Recognition of Previously Deferred Amounts	$ 0	$ (1)	$ (1)