Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Reported tax rate	5.30%		8.50%	(14.10%)	(2.00%)
Income Tax Uncertainties [Abstract]
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities		$ 303
Unrecognized Tax Benefits, Interest on Income Taxes Accrued		$ 307
Tax Adjustments, Settlements, and Unusual Provisions				$ 250
Unrecognized Tax Benefits	$ 511			511		$ 1,238
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	438			$ 438		$ 1,150
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				21.00%		35.00%
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	81			$ 81		$ 655
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	3		$ 14	22	$ 40
Tax Cuts and Jobs Act, Measurement Period Adjustment, Income Tax Expense (Benefit)				37
Tax Cuts and Jobs Act, Incomplete Accounting, Provisional Income Tax Expense (Benefit)				824
Tax Cuts and Jobs Act, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit)						$ 99
Tax Cuts and Jobs Act, Incomplete Accounting, Transition Tax for Accumulated Foreign Earnings, Provisional Liability				866
Tax Cuts and Jobs Act, Incomplete Accounting, Transition Tax for Accumulated Foreign Earnings, Provisional Liability Net Existing				506
Settlement with Taxing Authority [Member]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible within 12 Months	$ 226			$ 226