Quarterly Operating Results (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Condensed Statement of Earnings
Revenues	$ 1,283	$ 1,335	$ 1,093	$ 1,039	$ 1,156	$ 1,255	$ 1,052	$ 1,034	$ 4,750	$ 4,497	$ 4,320
Net earnings, including noncontrolling interests	127	107	37	49	109	126	100	88	320	423	530
Net earnings attributable to shareholders	$ 109	$ 96	$ 55	$ 83	$ 133	$ 132	$ 108	$ 106	$ 343	$ 479	$ 519
Earnings Attributable to Shareholders per Common Share:
Basic	$ 1.11	$ 0.96	$ 0.53	$ 0.80	$ 1.24	$ 1.22	$ 0.98	$ 0.94	$ 3.39	$ 4.38	$ 4.49
Diluted	$ 1.10	$ 0.94	$ 0.52	$ 0.79	$ 1.23	$ 1.21	$ 0.97	$ 0.93	$ 3.33	$ 4.33	$ 4.45
Average number of Common Shares:
Basic	98.2	99.7	102.7	104.6	106.7	108.2	110.2	112.0	101.3	109.2	115.7
Diluted	99.8	101.3	104.4	106.2	108.1	109.5	111.8	113.1	102.9	110.5	116.8