Risk Management Debt Fair Value Adjustment (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Amount the fair value of debt adjustment was decreased by related to unamortized debt discounts	$ 36	$ 33
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge	478	490
Amount the adjustment to fair value of debt was increased by related to the fair value of interest rate swaps	576	664
Increase (decrease) in debt fair value adjustment related to purchase accounting	$ 1,431	$ 1,470

Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective interest rate fair value hedge that is amortized upon discontinuation of the interest rate fair value hedge.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 25

-Section 35

-Paragraph 9

-URI http://asc.fasb.org/extlink&oid=6439857&loc=d3e75592-113984

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 24

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_DeferredGainLossOnDiscontinuationOfInterestRateFairValueHedge
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant