Segment and Geographic Information (Information Concerning Principal Geographic Areas) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 5,437	$ 4,861	$ 4,651
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ 380	$ 391	$ 413	$ 397	$ 431	$ 417	$ 263	$ 282	1,581	1,393	1,246
Net Income (Loss) Attributable to Parent	248	$ 209	$ 360	$ 250	263	$ 268	$ 182	$ 576	1,067	1,289	1,150
Identifiable Assets	163,488				158,554				163,488	158,554	151,604
Long-Lived Assets	11,846				16,506				11,846	16,506	19,735
Foreign [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									90	99	126
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									44	51	54
Net Income (Loss) Attributable to Parent									30	512	186
Identifiable Assets	800				869				800	869	2,891
Long-Lived Assets	0				0				0	0	0
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									90	98	124
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									44	47	54
Net Income (Loss) Attributable to Parent									32	35	68
Identifiable Assets	499				514				499	514	590
Long-Lived Assets	0				0				0	0	0
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									0	1	2
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									0	4	0
Net Income (Loss) Attributable to Parent									(1)	27	4
Identifiable Assets	276				325				276	325	1,636
Long-Lived Assets	0				0				0	0	0
Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									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									(1)	(2)	(8)
Identifiable Assets	23				28				23	28	29
Long-Lived Assets	0				0				0	0	0
Asia-Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									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	452	122
Identifiable Assets	2				2				2	2	636
Long-Lived Assets	0				0				0	0	0
Domestic [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									5,347	4,762	4,525
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest									1,537	1,342	1,192
Net Income (Loss) Attributable to Parent									1,037	777	964
Identifiable Assets	162,688				157,685				162,688	157,685	148,713
Long-Lived Assets	$ 11,846				$ 16,506				$ 11,846	$ 16,506	$ 19,735