Segment and Geographic Information Segment and Geographic Information (Information Concerning Principal Geographic Areas) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net	$ 1,473	$ 1,462	$ 1,455	$ 1,375	$ 1,368	$ 1,384	$ 1,358	$ 1,327	$ 5,765	$ 5,437	$ 4,861
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	410	395	376	326	380	391	413	397	1,507	1,581	1,393
Net Income (Loss) Attributable to Parent	181	$ 282	$ 252	$ 214	248	$ 209	$ 360	$ 250	929	1,067	1,289
Identifiable Assets	166,908				163,488				166,908	163,488	158,554
Long-Lived Assets	9,197				11,846				9,197	11,846	16,506
CANADA
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									89	90	98
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									42	44	47
Net Income (Loss) Attributable to Parent									37	32	35
Identifiable Assets	406				499				406	499	514
Long-Lived Assets	0				0				0	0	0
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									0	0	1
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									(1)	0	4
Net Income (Loss) Attributable to Parent									(6)	(1)	27
Identifiable Assets	315				276				315	276	325
Long-Lived Assets	0				0				0	0	0
Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									0	0	0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									0	0	0
Net Income (Loss) Attributable to Parent									0	(1)	(2)
Identifiable Assets	23				23				23	23	28
Long-Lived Assets	0				0				0	0	0
Asia Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									0	0	0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									0	0	0
Net Income (Loss) Attributable to Parent									0	0	452
Identifiable Assets	2				2				2	2	2
Long-Lived Assets	0				0				0	0	0
Foreign [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									89	90	99
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									41	44	51
Net Income (Loss) Attributable to Parent									31	30	512
Identifiable Assets	746				800				746	800	869
Long-Lived Assets	0				0				0	0	0
Domestic [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									5,676	5,347	4,762
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									1,466	1,537	1,342
Net Income (Loss) Attributable to Parent									898	1,037	777
Identifiable Assets	166,162				162,688				166,162	162,688	157,685
Long-Lived Assets	$ 9,197				$ 11,846				$ 9,197	$ 11,846	$ 16,506