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Net Income Per Common Share (Calculations For Basic And Diluted Earnings Per Share) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income—basic and diluted	$ 167us-gaap_NetIncomeLoss	$ 183us-gaap_NetIncomeLoss	$ 84us-gaap_NetIncomeLoss	$ 91us-gaap_NetIncomeLoss	$ 122us-gaap_NetIncomeLoss	$ 131us-gaap_NetIncomeLoss	$ 110us-gaap_NetIncomeLoss	$ 154us-gaap_NetIncomeLoss	$ 525us-gaap_NetIncomeLoss	$ 517us-gaap_NetIncomeLoss	$ 421us-gaap_NetIncomeLoss
Denominator:
Basic weighted-average common shares outstanding									163.5	163.5	162.5
Diluted weighted-average shares									165.1	165.4	163.7
Earnings per share:
Basic (in usd per share)	$ 1.03us-gaap_EarningsPerShareBasic	$ 1.12us-gaap_EarningsPerShareBasic	$ 0.51us-gaap_EarningsPerShareBasic	$ 0.56us-gaap_EarningsPerShareBasic	$ 0.75us-gaap_EarningsPerShareBasic	$ 0.80us-gaap_EarningsPerShareBasic	$ 0.67us-gaap_EarningsPerShareBasic	$ 0.95us-gaap_EarningsPerShareBasic	$ 3.21us-gaap_EarningsPerShareBasic	$ 3.16us-gaap_EarningsPerShareBasic	$ 2.59us-gaap_EarningsPerShareBasic
Diluted (in usd per share)	$ 1.02us-gaap_EarningsPerShareDiluted	$ 1.11us-gaap_EarningsPerShareDiluted	$ 0.51us-gaap_EarningsPerShareDiluted	$ 0.55us-gaap_EarningsPerShareDiluted	$ 0.74us-gaap_EarningsPerShareDiluted	$ 0.79us-gaap_EarningsPerShareDiluted	$ 0.66us-gaap_EarningsPerShareDiluted	$ 0.94us-gaap_EarningsPerShareDiluted	$ 3.18us-gaap_EarningsPerShareDiluted	$ 3.12us-gaap_EarningsPerShareDiluted	$ 2.57us-gaap_EarningsPerShareDiluted
Number of anti-dilutive stock-based awards									0.7	0.4	5.9
Stock Options
Denominator:
Effect of stock-based awards									1.0	1.2	0.5
Restricted Stock Units (RSUs)
Denominator:
Effect of stock-based awards									0.6	0.7	0.7