Schedule I - Parent Company Financial Information (Condensed Statements of Income) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues:
Total revenues	$ 9,557	$ 9,651	$ 9,699	[1]	$ 10,219	$ 9,056	$ 9,301	$ 9,284	$ 9,191	$ 39,126	$ 36,832	$ 33,596
Expenses:
Operating costs										5,830	5,395	4,380
Depreciation										263	249	225
Interest										105	109	105
(Benefit) provision for income taxes										689	816	650
Net income	192	426	356	[1]	248	199	445	460	315	1,222	1,419	1,099
Parent Company
Revenues:
Management fees charged to operating subsidiaries										1,220	1,272	1,175
Investment and other income, net										5	8	14
Total revenues										1,225	1,280	1,189
Expenses:
Operating costs										1,229	1,270	956
Depreciation										172	164	166
Interest										106	107	103
Total operating expense										1,507	1,541	1,225
Loss before income taxes and equity in net earnings of subsidiaries										(282)	(261)	(36)
(Benefit) provision for income taxes										(102)	(81)	35
Loss before equity in net earnings of subsidiaries										(180)	(180)	(71)
Equity in net earnings of subsidiaries										1,402	1,599	1,170
Net income										$ 1,222	$ 1,419	$ 1,099

[1] Includes an expense of $46 million ($29 million after tax, or $0.18 per diluted common share) for a litigation settlement associated with our military services business.