Quarterly Operating Results (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Statement of Earnings
Revenues	$ 1,626	$ 1,684	$ 1,541	$ 1,294	$ 1,549	$ 1,581	$ 1,392	$ 1,211	$ 6,145	$ 5,733	$ 5,103
Net earnings, including noncontrolling interests	130	66	149	25	125	91	83	107	370	406	453
Net earnings attributable to shareholders	$ 129	$ 63	$ 141	$ 19	$ 127	$ 116	$ 106	$ 103	$ 352	$ 452	$ 471
Earnings Attributable to Shareholders per Common Share:
Basic (USD per share)	$ 1.48	$ 0.72	$ 1.60	$ 0.22	$ 1.44	$ 1.30	$ 1.18	$ 1.15	$ 4.02	$ 5.07	$ 5.27
Diluted (USD per share)	$ 1.45	$ 0.71	$ 1.57	$ 0.21	$ 1.41	$ 1.28	$ 1.15	$ 1.13	$ 3.94	$ 4.97	$ 5.16
Average number of Common Shares:
Basic (shares)	87.4	87.5	87.7	87.6	87.9	89.0	89.6	89.6	87.6	89.0	89.3
Diluted (shares)	89.2	89.3	89.5	89.4	89.8	90.9	91.6	91.6	89.4	91.0	91.2