Income Taxes (Unrecognized Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1	$ 199	$ 206	$ 293
Additions, based on tax positions related to current year	7	7	8
Additions for tax positions of prior years	39	10	28
Reductions for tax positions of prior years	(91)	(6)	(4)
Reductions due to reclassification of tax indemnifications on sale of Kroll	0	(3)	0
Settlements	(6)	(4)	(4)
Lapses in statutes of limitation	(5)	(11)	(115)
Balance at December 31	$ 143	$ 199	$ 206