The cash outflow to acquire debt and equity securities not classified as either held-to-maturity securities or trading securities which would be classified as available-for-sale securities and reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

Name:	us-gaap_PaymentsToAcquireAvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Investments (Fair Value Method Investments) (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Snap [Member]
Schedule of Fair Value Method Investments [Line Items]
Payments to acquire available-for-sale securities		$ 500
NBCUniversal Media LLC [Member]
Schedule of Fair Value Method Investments [Line Items]
Contributed investment from Comcast			$ 662	$ 3,655	$ 252
NBCUniversal Media LLC [Member] \| Snap [Member]
Schedule of Fair Value Method Investments [Line Items]
Contributed investment from Comcast	$ 662