Business Combinations, Intangibles and Goodwill - Additional Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015 acquisition	Mar. 31, 2014	Dec. 31, 2014
Business Acquisition [Line Items]
Cash paid	$ 49	$ 1,068
Number of Businesses Acquired	2us-gaap_NumberOfBusinessesAcquired
Aggregate allocation to goodwill	16,174us-gaap_Goodwill		16,134us-gaap_Goodwill
All 2015 Acquisitions
Business Acquisition [Line Items]
Aggregate consideration	49
Aggregate allocation to goodwill	38
Aggregate allocation to intangibles	16
Aggregate allocation to net liabilities	$ (5)
Weighted average amortization period of intangible assets acquired	3 years 6 months 20 days

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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The amount of identifiable intangible assets recognized as of the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The number of businesses acquired by the entity during the period.

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The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

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