Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3044-108585

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Financial Instruments
Cash and cash equivalents	$ 772	$ 715	$ 337	$ 212
Institutional and Other \| Minimum
Financial Instruments
Fair value assumption, interest rate	3.19%	3.19%
Institutional and Other \| Maximum
Financial Instruments
Fair value assumption, interest rate	7.84%	7.51%
Fair Value \| Level 1
Financial Instruments
Cash and cash equivalents	$ 772	$ 715
Fair Value \| Level 2 \| Retail
Financial Instruments
Long-term debt	933	929
Fair Value \| Level 2 \| Institutional
Financial Instruments
Long-term debt	485	501
Fair Value \| Level 2 \| Other
Financial Instruments
Long-term debt	211	214
Book Value
Financial Instruments
Cash and cash equivalents	772	715
Book Value \| Retail
Financial Instruments
Long-term debt	917	917
Book Value \| Institutional
Financial Instruments
Long-term debt	533	533
Book Value \| Other
Financial Instruments
Long-term debt	$ 211	$ 214