Fair Value Measurements (Fair Value Of Assets And Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets:
Available-for-sale securities, fair value	$ 200	$ 166
Liabilities:
Foreign exchange derivative contracts	3	5
Interest agreement derivative contracts	4	3
U.S. Government And Agency Obligations [Member]
Assets:
Available-for-sale securities, fair value	16	16
Corporate Bonds [Member]
Assets:
Available-for-sale securities, fair value	10	10
Mortgage-Backed Bonds [Member]
Assets:
Available-for-sale securities, fair value	2	2
Common Stock And Equivalents [Member]
Assets:
Available-for-sale securities, fair value	48	11
Level 1 [Member]
Liabilities:
Foreign exchange derivative contracts	0	0
Interest agreement derivative contracts	0	0
Level 2 [Member]
Liabilities:
Foreign exchange derivative contracts	3	5
Interest agreement derivative contracts	4	3
Sigma Fund Securities [Member] | U.S. Government And Agency Obligations [Member]
Assets:
Sigma Fund securities, fair value	1,916	2,944
Sigma Fund Securities [Member] | Foreign Exchange Contracts [Member]
Assets:
Sigma Fund securities, fair value	1	1
Sigma Fund Securities [Member] | Level 1 [Member] | U.S. Government And Agency Obligations [Member]
Assets:
Sigma Fund securities, fair value	0	0
Sigma Fund Securities [Member] | Level 1 [Member] | Foreign Exchange Contracts [Member]
Assets:
Sigma Fund securities, fair value	0	0
Sigma Fund Securities [Member] | Level 2 [Member] | U.S. Government And Agency Obligations [Member]
Assets:
Sigma Fund securities, fair value	1,916	2,944
Sigma Fund Securities [Member] | Level 2 [Member] | Foreign Exchange Contracts [Member]
Assets:
Sigma Fund securities, fair value	1	1
Available-For-Sale Securities [Member] | U.S. Government And Agency Obligations [Member]
Assets:
Available-for-sale securities, fair value	16	16
Available-For-Sale Securities [Member] | Corporate Bonds [Member]
Assets:
Available-for-sale securities, fair value	10	10
Available-For-Sale Securities [Member] | Mortgage-Backed Bonds [Member]
Assets:
Available-for-sale securities, fair value	2	2
Available-For-Sale Securities [Member] | Common Stock And Equivalents [Member]
Assets:
Available-for-sale securities, fair value	48	11
Available-For-Sale Securities [Member] | Level 1 [Member] | U.S. Government And Agency Obligations [Member]
Assets:
Available-for-sale securities, fair value	0	0
Available-For-Sale Securities [Member] | Level 1 [Member] | Corporate Bonds [Member]
Assets:
Available-for-sale securities, fair value	0	0
Available-For-Sale Securities [Member] | Level 1 [Member] | Mortgage-Backed Bonds [Member]
Assets:
Available-for-sale securities, fair value	0	0
Available-For-Sale Securities [Member] | Level 1 [Member] | Common Stock And Equivalents [Member]
Assets:
Available-for-sale securities, fair value	40	3
Available-For-Sale Securities [Member] | Level 2 [Member] | U.S. Government And Agency Obligations [Member]
Assets:
Available-for-sale securities, fair value	16	16
Available-For-Sale Securities [Member] | Level 2 [Member] | Corporate Bonds [Member]
Assets:
Available-for-sale securities, fair value	10	10
Available-For-Sale Securities [Member] | Level 2 [Member] | Mortgage-Backed Bonds [Member]
Assets:
Available-for-sale securities, fair value	2	2
Available-For-Sale Securities [Member] | Level 2 [Member] | Common Stock And Equivalents [Member]
Assets:
Available-for-sale securities, fair value	$ 8	$ 8