Cash, Cash Equivalents, and Marketable Securities Cash, Cash Equivalents, and Marketable Securities - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Investments, Warrant Assets
Gain (loss) on Equity Warrant Assets	$ 15	$ 5
Level 2 Securities
Investments, Warrant Assets
Equity Warrant Assets	$ 257		$ 223

Value of outstanding derivative securities that permit the holder the right to purchase securities (usually equity) from the issuer at a specified price.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Name:	us-gaap_WarrantsAndRightsOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant