Quarterly Operating Results (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Statement of Earnings
Revenues	$ 1,529	$ 1,581	$ 1,392	$ 1,211	$ 1,362	$ 1,443	$ 1,139	$ 1,148	$ 5,713	$ 5,092	$ 4,957
Net earnings, including noncontrolling interests	125	91	83	107	165	98	77	113	406	453	402
Net earnings attributable to shareholders	$ 127	$ 116	$ 106	$ 103	$ 158	$ 83	$ 110	$ 120	$ 452	$ 471	$ 488
Earnings Attributable to Shareholders per Common Share:
Basic (USD per share)	$ 1.44	$ 1.30	$ 1.18	$ 1.15	$ 1.77	$ 0.94	$ 1.23	$ 1.34	$ 5.07	$ 5.27	$ 5.18
Diluted (USD per share)	$ 1.41	$ 1.28	$ 1.15	$ 1.13	$ 1.73	$ 0.92	$ 1.20	$ 1.32	$ 4.97	$ 5.16	$ 5.09
Average number of Common Shares:
Basic (shares)	87.9	89.0	89.6	89.6	89.4	89.1	89.6	89.4	89.0	89.3	94.2
Diluted (shares)	89.8	90.9	91.6	91.6	91.4	91.0	91.5	91.0	91.0	91.2	95.9