Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Summary of Significant Accounting Policies (Details 5) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
New Accounting Pronouncement, Early Adoption [Line Items]
Net income	$ 321,000,000	$ 268,000,000	$ 238,000,000	$ 247,000,000	$ 216,000,000	$ 245,000,000	$ 256,000,000	$ 253,000,000	$ 1,074,000,000	$ 970,000,000	$ 964,000,000
Total current assets	1,602,000,000				1,683,000,000				1,602,000,000	1,683,000,000
Other assets, net	92,000,000				100,000,000				92,000,000	100,000,000
Long-term debt, excluding current maturities	6,997,000,000				7,152,000,000				6,997,000,000	7,152,000,000
Deferred income taxes, net	$ 1,896,000,000				2,085,000,000				$ 1,896,000,000	2,085,000,000
Restatement adjustment | New accounting pronouncement, early adoption, effect
New Accounting Pronouncement, Early Adoption [Line Items]
Net income										0	0
Total current assets					(163,000,000)					(163,000,000)
Other assets, net					(109,000,000)					(109,000,000)
Long-term debt, excluding current maturities					(110,000,000)					(110,000,000)
Deferred income taxes, net					$ (162,000,000)					(162,000,000)
Net cash provided by (used in) operating activities										$ 0	$ 0