Debt (Fair Value of Debt) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Portion at Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	$ 5,418		$ 5,317
Loans Payable, Fair Value Disclosure	2,826		2,845
Notes Payable, Other Payables, Disclosure	1,751	[1]	1,772	[1]
Subsidiaries Term Loan	1,590		1,179
Debt Excluding Capital Leases	11,585		11,113
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	4,989		4,989
Loans Payable, Fair Value Disclosure	2,821		2,828
Notes Payable, Other Payables, Disclosure	1,743	[1]	1,766	[1]
Subsidiaries Term Loan	1,607		1,191
Debt Excluding Capital Leases	$ 11,160		$ 10,774

[1] Excludes a lease that is accounted for as a failed sale-leaseback transaction under U.S. GAAP.