Software development and intellectual property licenses (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Software development and intellectual property licenses:
Internally developed software costs	$ 168		$ 168		$ 115
Payments made to third-party software developers	152		152		84
Total software development costs	320		320		199
Intellectual property licenses	17		17		34
Amortization, write-offs and impairments:
Amortization of capitalized software development costs and intellectual property licenses	22	28	121	158
Write-offs and impairments	$ 0	$ 0	$ 8	$ 0