Quarterly Operating Results (Unaudited) (Details) (USD $) In Millions, except Per Share data, 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
Condensed Statement of Earnings
Revenues	$ 1,236	$ 1,563	$ 1,150	$ 1,113	$ 1,283	$ 1,335	$ 1,093	$ 1,039	$ 5,062	$ 4,750	$ 4,497
Net earnings, including noncontrolling interests	19	211	84	88	127	108	30	54	402	319	426
Net earnings attributable to shareholders	$ 50	$ 226	$ 99	$ 113	$ 109	$ 97	$ 48	$ 88	$ 488	$ 342	$ 482
Earnings Attributable to Shareholders per Common Share:
Basic	$ 0.55	$ 2.43	$ 1.02	$ 1.16	$ 1.11	$ 0.97	$ 0.47	$ 0.84	$ 5.18	$ 3.37	$ 4.41
Diluted	$ 0.54	$ 2.39	$ 1.01	$ 1.14	$ 1.09	$ 0.95	$ 0.46	$ 0.83	$ 5.09	$ 3.32	$ 4.36
Average number of Common Shares:
Basic	89.8	92.9	96.4	97.7	98.2	99.7	102.7	104.6	94.2	101.3	109.2
Diluted	91.4	94.6	98.0	99.4	99.8	101.3	104.4	106.2	95.9	102.9	110.5