Leases Rentals and Outsourced Service Arrangements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Leases Rentals And Outsourced Service Arrangements [Line Items]
Term length for operating leases	9 years
Rental expense for operating leases	$ 130	$ 115	$ 127
Future net minimum rental payments under non-cancelable operating leases	570
Future minimum rental payments under non-cancelable operating leases payable in one year	116
Future minimum rental payments under non-cancelable operating leases payable in two years	108
Future minimum rental payments under non-cancelable operating leases payable in three years	82
Future minimum rental payments under non-cancelable operating leases payable in four years	65
Future minimum rental payments under non-cancelable operating leases payable in five years	43
Future minimum rental payments under non-cancelable operating leases payable after five years	156
Other operating expenses related to outsourced service arrangements	$ 86	$ 116	$ 114
Minimum [Member]
Leases Rentals And Outsourced Service Arrangements [Line Items]
Initial service period under outsourced service arrangements	7 years
Maximum [Member]
Leases Rentals And Outsourced Service Arrangements [Line Items]
Initial service period under outsourced service arrangements	8 years