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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Statement of Earnings
Revenues	$ 2,623	$ 2,060	$ 1,951	$ 1,275	$ 2,130	$ 2,123	$ 1,960	$ 2,024	$ 7,909	$ 8,237	$ 7,150
Net earnings, including noncontrolling interests	694	164	167	(304)	191	143	209	326	721	869	517
Net earnings (loss) attributable to shareholders	$ 692	$ 164	$ 177	$ (301)	$ 211	$ 147	$ 210	$ 329	$ 732	$ 897	$ 530
Earnings Attributable to Shareholders per Common Share:
Basic (USD per share)	$ 7.99	$ 1.86	$ 1.98	$ (3.34)	$ 2.33	$ 1.64	$ 2.34	$ 3.68	$ 8.25	$ 9.98	$ 5.95
Diluted (USD per share)	$ 7.93	$ 1.86	$ 1.97	$ (3.34)	$ 2.31	$ 1.62	$ 2.31	$ 3.63	$ 8.20	$ 9.85	$ 5.85
Average number of Common Shares:
Basic (shares)	86.6	88.2	89.7	90.3	90.2	90.0	89.7	89.4	88.7	89.9	89.0
Diluted (shares)	87.2	88.5	90.0	90.3	91.3	91.1	91.0	90.7	89.2	91.0	90.6