Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Income Taxes
Effective tax rate on income from continuing operations (as a percent)	22.50%	20.70%
Valuation allowance	$ 20		$ 20
Gross unrecognized tax benefit (expense)	241us-gaap_UnrecognizedTaxBenefits		242us-gaap_UnrecognizedTaxBenefits
Unrecognized tax benefits (net of federal tax benefits) that would impact the effective tax rate	55		57
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, lower bound	170
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, upper bound	180
Increase (reduction) in interest and penalties	1	(1)
Accrued interest and penalties	49		48
State and Local [Member]
Income Taxes
State net operating losses	$ 25

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The amount of estimated penalties and interest accrued as of the balance sheet date arising from income tax examinations.

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Amount of (increase) decrease reasonably possible in the estimated lower bound of the unrecognized tax benefit for a tax position taken or expected to be taken.

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Amount of (increase) decrease reasonably possible in the estimated upper bound of the unrecognized tax benefit for a tax position taken or expected to be taken.

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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