Pension Plans, Retirement Benefits and Savings Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	$ 4,195	$ 3,659
Benefits earned	133	118	$ 133
Interest cost on benefit obligation	114	141	126
Actuarial (gain) loss	356	470
Benefits paid	(212)	(198)
Amendment	1	0
Foreign currency exchange rate change, change in projected benefit obligation	4	5
Benefit obligation, balance, end of year	4,591	4,195	3,659
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	4,385	3,874
Actual return on plan assets	570	696
Company contributions	9	8
Benefits paid	(212)	(198)
Foreign currency exchange rate change, change in plan assets	4	5
Fair value of plan assets, balance, end of year	4,756	4,385	3,874
Funded status of plan at end of year	165	190
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	306	317
Accrued under-funded benefit plan liabilities	(141)	(127)
Total amount recognized in the consolidated balance sheet	165	190
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss (gain)	1,113	1,143
Prior service cost (benefit)	(1)	(3)
Total amount recognized in accumulated other comprehensive income	1,112	1,140
Pension Plans [Member] | United States [Member] | Qualified Plan [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	3,954	3,444
Benefits earned	128	112
Interest cost on benefit obligation	109	134
Actuarial (gain) loss	336	451
Benefits paid	(201)	(187)
Amendment	0	0
Foreign currency exchange rate change, change in projected benefit obligation	0	0
Benefit obligation, balance, end of year	4,326	3,954	3,444
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	4,270	3,771
Actual return on plan assets	562	686
Company contributions	0	0	200
Benefits paid	(201)	(187)
Foreign currency exchange rate change, change in plan assets	0	0
Fair value of plan assets, balance, end of year	4,631	4,270	3,771
Funded status of plan at end of year	305	316
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	305	316
Accrued under-funded benefit plan liabilities	0	0
Total amount recognized in the consolidated balance sheet	305	316
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss (gain)	1,050	1,094
Prior service cost (benefit)	(2)	(3)
Total amount recognized in accumulated other comprehensive income	1,048	1,091
Nonqualified and Foreign Pension Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	241	215
Benefits earned	5	6
Interest cost on benefit obligation	5	7
Actuarial (gain) loss	20	19
Benefits paid	(11)	(11)
Amendment	1	0
Foreign currency exchange rate change, change in projected benefit obligation	4	5
Benefit obligation, balance, end of year	265	241	215
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	115	103
Actual return on plan assets	8	10
Company contributions	9	8
Benefits paid	(11)	(11)
Foreign currency exchange rate change, change in plan assets	4	5
Fair value of plan assets, balance, end of year	125	115	103
Funded status of plan at end of year	(140)	(126)
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	1	1
Accrued under-funded benefit plan liabilities	(141)	(127)
Total amount recognized in the consolidated balance sheet	(140)	(126)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss (gain)	63	49
Prior service cost (benefit)	1	0
Total amount recognized in accumulated other comprehensive income	64	49
Postretirement Benefit Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	171	203
Benefits earned	0	0	0
Interest cost on benefit obligation	4	7	7
Actuarial (gain) loss	5	(31)
Benefits paid	(10)	(9)
Foreign currency exchange rate change, change in projected benefit obligation	1	1
Benefit obligation, balance, end of year	171	171	203
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	12	12
Actual return on plan assets	1	1
Company contributions	8	8
Benefits paid	(10)	(9)
Fair value of plan assets, balance, end of year	11	12	$ 12
Funded status of plan at end of year	(160)	(159)
Amounts recognized in the consolidated balance sheet consist of:
Accrued under-funded benefit plan liabilities	(160)	(159)
Total amount recognized in the consolidated balance sheet	(160)	(159)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss (gain)	(41)	(49)
Prior service cost (benefit)	(18)	(21)
Total amount recognized in accumulated other comprehensive income	$ (59)	$ (70)