Equity (Details 5) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other disclosures
Total share-based compensation expense included in net income	$ 12	$ 12	$ 11
Share-based payments subject to redemption	24	19
Long Term Incentive Plan for Officers
Weighted-average grant date fair value
Unrecognized compensation cost	3
Other disclosures
Service period over which compensation expense would be amortized	3 years
Total share-based compensation expense included in net income	3	4	6
Share-based payments subject to redemption	7	8
Long Term Incentive Plan for Officers | Minimum
Weighted-average grant date fair value
Weighted-average period for amortization of unrecognized compensation cost	1 year
Long Term Incentive Plan for Officers | Maximum
Weighted-average grant date fair value
Weighted-average period for amortization of unrecognized compensation cost	2 years
Board of Directors' Compensation Arrangement
Other disclosures
Minimum percentage of Board of Director's compensation they may elect to be awarded in the form of common stock or restricted stock units	50.00%
Restricted Shares and Restricted Stock Units
Other disclosures
Total share-based compensation expense included in net income	7	6	4
Compensation cost related to unvested restricted share and restricted stock units included in share-based payments subject to redemption on the Balance Sheet	17	11
Restricted Shares and Restricted Stock Units | Minimum
Equity stock-based compensation
Vesting terms	3 years
Restricted Shares and Restricted Stock Units | Maximum
Equity stock-based compensation
Vesting terms	5 years
Restricted Shares
Restricted shares and unit activity
Non-vested at the beginning of the period (in shares)	95,000	136,000	181,000
Vested (in shares)	(33,000)	(37,000)	(34,000)
Cancelled (in shares)	(14,000)	(4,000)	(11,000)
Non-vested at the end of the period (in shares)	48,000	95,000	136,000
Weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 29.69	$ 30.69	$ 30.04
Vested (in dollars per share)	$ 34.02	$ 33.73	$ 27.56
Cancelled (in dollars per share)	$ 31.25	$ 25.58	$ 29.74
Non-vested at the end of the period (in dollars per share)	$ 26.25	$ 29.69	$ 30.69
Fair value of awards vested during the year	1.0	1.0	1.0
Restricted Units
Restricted shares and unit activity
Non-vested at the beginning of the period (in shares)	385,000	235,000	113,000
Granted (in shares)	144,000	174,000	182,000
Vested (in shares)	(17,000)	(9,000)	(56,000)
Cancelled (in shares)	(43,000)	(15,000)	(4,000)
Non-vested at the end of the period (in shares)	469,000	385,000	235,000
Weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 49.77	$ 44.24	$ 30.56
Granted (in dollars per share)	$ 66.27	$ 55.69	$ 48.04
Vested (in dollars per share)	$ 46.82	$ 37.57	$ 26.08
Cancelled (in dollars per share)	$ 54.93	$ 44.95	$ 47.98
Non-vested at the end of the period (in dollars per share)	$ 54.47	$ 49.77	$ 44.24
Fair value of awards vested during the year	1.0	0.3	1.0
Unrecognized compensation cost	10
Weighted-average period for amortization of unrecognized compensation cost	1 year 10 months 24 days
Restricted Units | Board of Directors' Compensation Arrangement
Other disclosures
Minimum period of restriction for transfer of award after director's termination of service from the board	6 months
Awards outstanding (in shares)	218,000
Carrying value of share units outstanding	$ 6