Income Taxes (Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Rollforward of Unrecognized Tax Benefits
Balance at beginning of period	$ 1,804	$ 2,228	$ 4,096
Increases based on tax positions related to the current period	172	230	135
Increases based on tax positions related to prior periods	14	114	100
Decreases based on tax positions related to prior periods	(134)	(753)	(2,080)
Decreases related to settlements with taxing authorities	0	(7)	(19)
Decreases related to a lapse of applicable statute of limitations	(5)	(8)	(4)
Balance at end of period	1,851	1,804	2,228
Unrecognized tax benefits that , if recognized, would favorably affect the effective tax rate in future periods	1,100	1,100	1,000
Recognized interest expense (benefit) (net of federal and state income tax benefits)	28	18	(35)
Interest expense accrued net of federal and state income tax benefits	$ 150	$ 122	$ 258

Interest expense accrued net of federal and state income tax benefits.

No definition available.

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- Definition

The net amount of nonoperating interest income (expense).

+ References

No definition available.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=SL6600010-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Unrecognized Tax Benefit
-URI http://asc.fasb.org/extlink&oid=6527854

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- Definition

Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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- Definition

Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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- Definition

Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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- Definition

Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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- Definition

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

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