Debt (Short Term Debt Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Short-term debt	$ 8,162,000,000		$ 7,962,000,000
Subsidiaries
Short-term Debt [Line Items]
Short-term debt	8,162,000,000		7,930,000,000
Accounts receivable facility | Accounts Receivable Securitization Facility
Short-term Debt [Line Items]
Average outstanding amount	$ 516,000,000
Interest rate during period	0.80%
Maximum month-end outstanding amount	$ 608,000,000
Line of credit facility, maximum borrowing capacity		$ 625,000,000
Extension period	364 days
Collateral amount	$ 620,000,000
Accounts receivable facility | Subsidiaries | Accounts Receivable Securitization Facility
Short-term Debt [Line Items]
Short-term debt	$ 571,000,000		$ 548,000,000