Pension Plans, Retirement Benefits and Savings Plans (details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	$ 3,592	$ 3,478
Benefits earned	119	118	$ 131
Interest cost on benefit obligation	127	122	144
Actuarial loss (gain)	259	69
Benefits paid	(187)	(177)
Settlement	(11)	(3)
Foreign currency exchange rate change, change in projected benefit obligation	10	(15)
Benefit obligation, balance, end of year	3,909	3,592	3,478
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	3,493	3,242
Actual return on plan assets	459	233
Company contributions	307	214
Benefits paid	(187)	(177)
Settlement	(12)	(3)
Foreign currency exchange rate change, change in plan assets	10	(16)
Fair value of plan assets, balance, end of year	4,070	3,493	3,242
Funded status of plan at end of year	161	(99)
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	284	25
Accrued under-funded benefit plan liabilities	(123)	(124)
Total amount recognized in the consolidated balance sheet	161	(99)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial (gain) loss	1,082	1,127
Prior service benefit	(6)	(6)
Total amount recognized in accumulated other comprehensive income	1,076	1,121
Pension Plans [Member] | United States [Member] | Qualified Plan [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	3,367	3,250
Benefits earned	112	111
Interest cost on benefit obligation	120	114
Actuarial loss (gain)	258	54
Benefits paid	(178)	(162)
Benefit obligation, balance, end of year	3,679	3,367	3,250
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	3,387	3,127
Actual return on plan assets	448	222
Company contributions	300	200	100
Benefits paid	(178)	(162)
Fair value of plan assets, balance, end of year	3,957	3,387	3,127
Funded status of plan at end of year	278	20
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	278	20
Total amount recognized in the consolidated balance sheet	278	20
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial (gain) loss	1,035	1,072
Prior service benefit	(6)	(6)
Total amount recognized in accumulated other comprehensive income	1,029	1,066
Nonqualified and Foreign Pension Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	225	228
Benefits earned	7	7
Interest cost on benefit obligation	7	8
Actuarial loss (gain)	1	15
Benefits paid	(9)	(15)
Settlement	(11)	(3)
Foreign currency exchange rate change, change in projected benefit obligation	10	(15)
Benefit obligation, balance, end of year	230	225	228
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	106	115
Actual return on plan assets	11	11
Company contributions	7	14
Benefits paid	(9)	(15)
Settlement	(12)	(3)
Foreign currency exchange rate change, change in plan assets	10	(16)
Fair value of plan assets, balance, end of year	113	106	115
Funded status of plan at end of year	(117)	(119)
Amounts recognized in the consolidated balance sheet consist of:
Accrued over-funded benefit plan assets	6	5
Accrued under-funded benefit plan liabilities	(123)	(124)
Total amount recognized in the consolidated balance sheet	(117)	(119)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial (gain) loss	47	55
Total amount recognized in accumulated other comprehensive income	47	55
Postretirement Benefit Plans [Member]
Change in projected benefit obligation [Roll Forward]
Benefit obligation, balance, beginning of year	214	233
Interest cost on benefit obligation	7	8	10
Actuarial loss (gain)	13	(17)
Benefits paid	(10)	(11)
Foreign currency exchange rate change, change in projected benefit obligation	1	1
Benefit obligation, balance, end of year	225	214	233
Change in plan assets [Roll Forward]
Fair value of plan assets, balance, beginning of year	14	15
Company contributions	9	10
Benefits paid	(10)	(11)
Fair value of plan assets, balance, end of year	13	14	$ 15
Funded status of plan at end of year	(212)	(200)
Amounts recognized in the consolidated balance sheet consist of:
Accrued under-funded benefit plan liabilities	(212)	(200)
Total amount recognized in the consolidated balance sheet	(212)	(200)
Amounts recognized in accumulated other comprehensive income consist of:
Net actuarial (gain) loss		(13)
Prior service benefit	(28)	(31)
Total amount recognized in accumulated other comprehensive income	$ (28)	$ (44)