Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Income tax expense		$ 138	$ 550	$ 186
Effective income tax rate		21.00%	35.00%	35.00%
Tax Cuts and Jobs Act of 2017, incomplete accounting, provisional income tax expense			$ 49
Tax Cuts and Jobs Act of 2017, incomplete accounting, transition tax for accumulated foreign earnings, provisional income tax expense			190
Effective income tax rate reconciliation, Tax Cuts and Jobs Act, additional income tax benefit	$ 54
Pension plan contributions, tax deductible	350
Effective income tax rate reconciliation, Tax Cuts and Jobs Act, additional income tax expense	95
Effective income tax rate reconciliation, Tax Cuts and Jobs Act, unrecognized tax benefits	55
U.S. transition tax expense recognized to date	285	$ 285
Earnings of foreign subsidiaries	2,800	2,800
Transition tax provision, deemed remittance	3,300	3,300
Cash and cash equivalents as presented in our Consolidated Balance Sheets	1,498	1,498	1,196	$ 1,085
Operating loss carryforwards	4,900	4,900
Operating loss carryforwards, not subject to expiration	3,200	3,200
U.S. general business credit carryforwards, including Energy Tax Credits	875	875	927
Valuation allowance, deferred tax assets	348	348	178
Valuation allowance, increase in deferred tax assets			75
Unrecognized tax benefits, income tax penalties and interest expense (benefit)		2	8	(19)
Unrecognized tax benefits, income tax penalties and interest accrued	46	46	45	$ 42
Unrecognized tax benefits	15	15
United States Pension Benefits
Cash and Cash Equivalents [Line Items]
Operating loss carryforwards	801	801
Net Operating Loss Carryforward
Cash and Cash Equivalents [Line Items]
Valuation allowance, deferred tax assets	286	286	156
Other Deferred Tax Assets
Cash and Cash Equivalents [Line Items]
Valuation allowance, deferred tax assets	$ 62	$ 62	$ 22