Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2036	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2013	Dec. 31, 2010	Dec. 31, 2007	Dec. 31, 2005	Dec. 31, 2004	Dec. 31, 2015
Income Tax Examination [Line Items]
Operating Loss Carryforwards, Valuation Allowance			$ 700
Valuation Allowance
Income tax loss carryforwards, subject to expiration			473
Remaining amount of loss carryforwards that has no expiration date			251
Unremitted earnings			8,900
Unrecognized tax benefits			251
Total accrued penalties and net accrued interest			47						$ 40
Aggregate resolution of uncertainties			$ 140
Year federal income tax returns have been audited			2013
Income Tax Examination, Year under Examination						2007	2005	2004
Minimum [Member]
Valuation Allowance
Income Tax Examination, Year under Examination					2010
Minimum [Member] | Scenario, Forecast
Valuation Allowance
Operating Loss Carryforwards, Expiration Date		Jan. 01, 2017
Maximum [Member]
Valuation Allowance
Income Tax Examination, Year under Examination				2013
Maximum [Member] | Scenario, Forecast
Valuation Allowance
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2036