Quarterly Operating Results (Unaudited) - Quarterly results of consolidated operations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Statement of Earnings
Revenues	$ 1,737	$ 1,705	$ 1,581	$ 1,475	$ 1,618	$ 1,687	$ 1,543	$ 1,297	$ 6,498	$ 6,145	$ 5,733
Net earnings, including noncontrolling interests	388	113	63	104	130	66	149	25	668	370	406
Net earnings attributable to shareholders	$ 385	$ 109	$ 54	$ 101	$ 129	$ 63	$ 141	$ 19	$ 649	$ 352	$ 452
Earnings Attributable to Shareholders per Common Share:
Basic (USD per share)	$ 4.43	$ 1.25	$ 0.63	$ 1.16	$ 1.48	$ 0.72	$ 1.60	$ 0.22	$ 7.47	$ 4.02	$ 5.07
Diluted (USD per share)	$ 4.33	$ 1.23	$ 0.62	$ 1.14	$ 1.45	$ 0.71	$ 1.57	$ 0.21	$ 7.33	$ 3.94	$ 4.97
Average number of Common Shares:
Basic (shares)	86.9	86.9	86.8	86.9	87.4	87.5	87.7	87.6	86.9	87.6	89.0
Diluted (shares)	88.8	88.5	88.4	88.5	89.2	89.3	89.5	89.4	88.5	89.4	91.0