Income Taxes Income Taxes (Schedule of Deferred tax assets and related valuation allowances recognized for net operating and other loss carryforwards and tax carryforwards) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	$ 2,002
Tax Credit Carryforward, Valuation Allowance	(983)
Net Deferred Tax Assets, Tax Credit Carryforwards	1,019
Deferred Tax Assets, Operating Loss Carryforwards	302
Operating Loss Carryforwards, Valuation Allowance	0
Net Deferred Tax Assets, Operating Loss Carryforwards	302
Deferred Tax Assets, Capital Loss Carryforwards	2
Capital Loss Carryforwards, Valuation Allowance	(2)
Net Deferred Tax Assets, Capital Loss Carryforwards	0
Deferred Tax Assets, State and Local Tax Carryforwards	557
State and Local Tax Carryforwards, Valuation Allowance	(137)
Net Deferred Tax Assets, State and Local Tax Carryforwards	420
Deferred Tax Assets, Other Non-Attribute	(983)
Other Non-Attribute, Valuation Allowance	(3)
Net Deferred Tax Assets, Other Non-Attribute	(986)
Deferred Tax Assets, Gross, Net of Deferred Tax Liabilities	1,576
Deferred Tax Assets, Valuation Allowance	(1,123)
Deferred Tax Assets, Net	461	$ 994
Foreign Tax Credits [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	1,772
Tax Credit Carryforward, Valuation Allowance	(983)
Net Deferred Tax Assets, Tax Credit Carryforwards	789
General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	213
Tax Credit Carryforward, Valuation Allowance	0
Net Deferred Tax Assets, Tax Credit Carryforwards	213
AMT Credits [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	17
Tax Credit Carryforward, Valuation Allowance	0
Net Deferred Tax Assets, Tax Credit Carryforwards	17
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	253
Operating Loss Carryforwards, Valuation Allowance	(135)
Net Deferred Tax Assets, Operating Loss Carryforwards	118
Net impacts as a result of the Tax Act [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Net	421
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	549
Deferred Tax Liability [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Net	$ 453	$ 976