Fair Value Measurement (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Assets at fair value:
Cash and cash equivalents	$ 317	$ 316
Fiduciary funds - restricted (included within Fiduciary assets)	1,957	1,764
Derivative financial instruments	50	47
Total assets	2,324	2,127
Liabilities at fair value:
Derivative financial instruments	14	12
Changes in fair value of hedged debt	16	12
Total liabilities	30	24
Quoted prices in active markets for identical assets Level 1 [Member]
Assets at fair value:
Cash and cash equivalents	317	316
Fiduciary funds - restricted (included within Fiduciary assets)	1,957	1,764
Derivative financial instruments	0	0
Total assets	2,274	2,080
Quoted prices in active markets for identical assets Level 1 [Member]
Liabilities at fair value:
Derivative financial instruments	0	0
Changes in fair value of hedged debt	0	0
Total liabilities	0	0
Significant other observable inputs Level 2 [Member]
Assets at fair value:
Cash and cash equivalents	0	0
Fiduciary funds - restricted (included within Fiduciary assets)	0	0
Derivative financial instruments	50	47
Total assets	50	47
Significant other observable inputs Level 2 [Member]
Liabilities at fair value:
Derivative financial instruments	14	12
Changes in fair value of hedged debt	16	12
Total liabilities	30	24
Significant other unobservable inputs Level 3 [Member]
Assets at fair value:
Cash and cash equivalents	0	0
Fiduciary funds - restricted (included within Fiduciary assets)	0	0
Derivative financial instruments	0	0
Total assets	0	0
Significant other unobservable inputs Level 3 [Member]
Liabilities at fair value:
Derivative financial instruments	0	0
Changes in fair value of hedged debt	0	0
Total liabilities	$ 0	$ 0