Pension Plans, Retirement Benefits and Savings Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	$ 3,909	$ 3,592
Benefits earned	133	119	$ 118
Interest cost on benefit obligation	126	127	122
Actuarial (gain) loss	(284)	259
Benefits paid	(219)	(187)
Settlement		(11)
Foreign currency exchange rate change, change in projected benefit obligation	(6)	10
Benefit obligation, balance, end of year	3,659	3,909	3,592
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	4,070	3,493
Actual return on plan assets	(180)	459
Company contributions	210	307
Benefits paid	(219)	(187)
Settlement		(12)
Foreign currency exchange rate change, change in plan assets	(7)	10
Fair value of plan assets, balance, end of year	3,874	4,070	3,493
Funded status of plan at end of year	215	161
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	331	284
Accrued under-funded benefit plan liabilities	(116)	(123)
Total amount recognized in the consolidated balance sheet	215	161
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss (gain)	1,149	1,082
Prior service benefit	(4)	(6)
Total amount recognized in accumulated other comprehensive income	1,145	1,076
Pension Plans [Member] | United States [Member] | Qualified Plan [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	3,679	3,367
Benefits earned	126	112
Interest cost on benefit obligation	119	120
Actuarial (gain) loss	(273)	258
Benefits paid	(207)	(178)
Benefit obligation, balance, end of year	3,444	3,679	3,367
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	3,957	3,387
Actual return on plan assets	(179)	448
Company contributions	200	300	200
Benefits paid	(207)	(178)
Fair value of plan assets, balance, end of year	3,771	3,957	3,387
Funded status of plan at end of year	327	278
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	327	278
Total amount recognized in the consolidated balance sheet	327	278
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss (gain)	1,113	1,035
Prior service benefit	(5)	(6)
Total amount recognized in accumulated other comprehensive income	1,108	1,029
Nonqualified and Foreign Pension Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	230	225
Benefits earned	7	7
Interest cost on benefit obligation	7	7
Actuarial (gain) loss	(11)	1
Benefits paid	(12)	(9)
Settlement		(11)
Foreign currency exchange rate change, change in projected benefit obligation	(6)	10
Benefit obligation, balance, end of year	215	230	225
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	113	106
Actual return on plan assets	(1)	11
Company contributions	10	7
Benefits paid	(12)	(9)
Settlement		(12)
Foreign currency exchange rate change, change in plan assets	(7)	10
Fair value of plan assets, balance, end of year	103	113	106
Funded status of plan at end of year	(112)	(117)
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	4	6
Accrued under-funded benefit plan liabilities	(116)	(123)
Total amount recognized in the consolidated balance sheet	(112)	(117)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss (gain)	36	47
Prior service benefit	1
Total amount recognized in accumulated other comprehensive income	37	47
Postretirement Benefit Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	225	214
Interest cost on benefit obligation	7	7	8
Actuarial (gain) loss	(18)	13
Benefits paid	(10)	(10)
Foreign currency exchange rate change, change in projected benefit obligation	(1)	1
Benefit obligation, balance, end of year	203	225	214
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	13	14
Company contributions	9	9
Benefits paid	(10)	(10)
Fair value of plan assets, balance, end of year	12	13	$ 14
Funded status of plan at end of year	(191)	(212)
Amounts recognized in the consolidated balance sheet consist of:
Accrued under-funded benefit plan liabilities	(191)	(212)
Total amount recognized in the consolidated balance sheet	(191)	(212)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial loss (gain)	(17)
Prior service benefit	(25)	(28)
Total amount recognized in accumulated other comprehensive income	$ (42)	$ (28)