Summary of Accounting Policies - Notes and Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Short-term and long-term accounts receivable outstanding	$ 1,293,000,000	$ 1,126,000,000
Allowance for doubtful accounts on short-term and long-term accounts receivable	16,000,000	16,000,000
Short and Long-term notes receivable outstanding	4,000,000	5,000,000
Allowance for doubtful accounts on short-term and long-term notes receivable	0	0
Capitalized Computer Software, Amortization	$ 12,000,000	$ 13,000,000	$ 15,000,000