Stock-Based Compensation (Summary of option activity under stock incentive plan and omnibus plan) (Details) - Stock Option - Stock Incentive Plan and Omnibus Plan - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Options, Outstanding [Roll Forward]
Outstanding at January 1, 2014 (in shares)	9,997,360
Granted (in shares)	500,000
Exercised (in shares)	(1,392,048)
Forfeited or Expired (in shares)	(209,791)
Outstanding at December 31, 2014 (in shares)	8,895,521	9,997,360
Exercisable at December 31, 2014 (in shares)	8,206,279
Weighted Average Exercise Price [Roll Forward]
Outstanding at January 1, 2014 (in dollars per share)	$ 11.55
Granted (in dollars per share)	22.75
Exercised (in dollars per share)	11.03
Forfeited or Expired (in dollars per share)	14.42
Outstanding at December 31, 2014 (in dollars per share)	12.62	$ 11.55
Exercisable at December 31, 2014 (in dollars per share)	$ 11.21
Additional Disclosures [Abstract]
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	3 years 7 months 6 days	4 years 6 months
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	3 years 7 months 6 days	4 years 6 months
Weighted average remaining contractual term, Exercisable at December 31, 2014	3 years 4 months 24 days
Aggregate intrinsic value. Outstanding at January 1, 2014	$ 170
Aggregate intrinsic value. Outstanding at December 31, 2014	106	$ 170
Aggregate intrinsic value, Exercisable at December 31, 2014	$ 102