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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Statement of Earnings
Revenues	$ 1,690	$ 2,008	$ 1,833	$ 1,619	$ 1,808	$ 1,835	$ 1,646	$ 1,576	$ 7,150	$ 6,865	$ 6,498
Net earnings, including noncontrolling interests	(35)	203	208	141	166	11	145	155	517	477	668
Net earnings (losses) attributable to shareholders	$ (29)	$ 204	$ 210	$ 145	$ 166	$ 11	$ 145	$ 153	$ 530	$ 475	$ 649
Earnings Attributable to Shareholders per Common Share:
Basic (USD per share)	$ (0.33)	$ 2.30	$ 2.36	$ 1.64	$ 1.88	$ 0.13	$ 1.64	$ 1.76	$ 5.95	$ 5.40	$ 7.47
Diluted (USD per share)	$ (0.33)	$ 2.26	$ 2.31	$ 1.60	$ 1.84	$ 0.13	$ 1.61	$ 1.72	$ 5.85	$ 5.28	$ 7.33
Average number of Common Shares:
Basic (shares)	89.3	89.1	89.0	88.6	88.2	88.1	87.8	87.2	89.0	87.8	86.9
Diluted (shares)	89.3	90.7	90.7	90.4	90.1	90.0	89.8	89.3	90.6	89.8	88.5