Stock Repurchase Plan (Details) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2014	Dec. 31, 2013
Stock Repurchase Plan (Details) [Abstract]
Authorized aggregate amount	$ 1,250,000,000
Total number of shares repurchased since inception of our stock repurchase program (shares)	36,994,653	36,994,653
Aggregate purchase price of shares repurchased since inception of our stock repurchase program	994,800,000	994,800,000
Number of shares repurchased (shares)	0
Purchase price of shares repurchased	$ 0

Stock repurchased and retired since inception of program (shares).

No definition available.

Name:	na_StockRepurchasedAndRetiredSinceInceptionOfProgramShares
Namespace Prefix:	na_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Stock repurchased and retired since inception of program (value).

+ References

No definition available.

+ Details

Name:	na_StockRepurchasedAndRetiredSinceInceptionOfProgramValue
Namespace Prefix:	na_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	na_StockRepurchasePlanDetailsAbstract
Namespace Prefix:	na_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares that have been repurchased and retired during the period.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

+ Details

Name:	us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

+ References

+ Details

Name:	us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of a stock repurchase plan authorized by an entity's Board of Directors.

+ References

No definition available.

+ Details

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