Segment and Geographic Information (Information Concerning Principal Geographic Areas) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 1,384	$ 1,302	$ 4,069	$ 3,522
Income (loss) from continuing operations before income tax expense	391	417	1,201	962
Net Income (Loss) Attributable to Parent	209	268	819	1,026
Foreign [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	22	24	67	77
Income (loss) from continuing operations before income tax expense	10	12	32	40
Net Income (Loss) Attributable to Parent	7	9	22	510
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	22	24	67	76
Income (loss) from continuing operations before income tax expense	10	11	32	35
Net Income (Loss) Attributable to Parent	9	9	27	30
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	0	0	0	1
Income (loss) from continuing operations before income tax expense	0	1	0	5
Net Income (Loss) Attributable to Parent	(1)	0	(4)	28
Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	0		0
Income (loss) from continuing operations before income tax expense	0		0
Net Income (Loss) Attributable to Parent	(1)		(1)
Asia-Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues				0
Income (loss) from continuing operations before income tax expense				0
Net Income (Loss) Attributable to Parent				452
Domestic [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	1,362	1,278	4,002	3,445
Income (loss) from continuing operations before income tax expense	381	405	1,169	922
Net Income (Loss) Attributable to Parent	$ 202	$ 259	$ 797	$ 516