Lease Obligations - Narrative (Details) (USD $) In Billions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Leases [Abstract]
Operating leases, rent expense	$ 1.2us-gaap_LeaseAndRentalExpense	$ 1.1us-gaap_LeaseAndRentalExpense	$ 1.1us-gaap_LeaseAndRentalExpense

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

No definition available.

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