Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Cash flows from operating activities:
Net earnings	$ 81,792		$ 4,322		$ 45,353
Adjustments to reconcile net earnings to operating cash flows:
Investment gains/losses	(71,123)		22,155		(1,410)
Depreciation and amortization	10,064		9,779		9,188
Other	(1,254)		2,957		458
Changes in operating assets and liabilities:
Losses and loss adjustment expenses	6,087		3,449		25,027
Deferred charges reinsurance assumed	357		1,174		(7,231)
Unearned premiums	1,707		1,794		1,761
Receivables and originated loans	(2,303)		(3,443)		(1,990)
Other assets	(2,011)		(1,832)		(1,665)
Other liabilities	190		2,002		1,194
Income taxes	15,181		(4,957)		(24,957)
Net cash flows from operating activities	38,687		37,400		45,728
Cash flows from investing activities:
Purchases of equity securities	(18,642)		(43,210)		(20,326)
Sales and redemptions of equity securities	14,336		18,783		19,512
Purchases of U.S. Treasury Bills and fixed maturity securities	(136,123)		(141,844)		(158,492)
Sales of U.S. Treasury Bills and fixed maturity securities	15,929		39,693		49,327
Redemptions and maturities of U.S. Treasury Bills and fixed maturity securities	137,767		113,045		86,727
Purchases of loans and finance receivables	(75)		(1,771)		(1,435)
Collections of loans and finance receivables	345		342		1,702
Acquisitions of businesses, net of cash acquired	(1,683)		(3,279)		(2,708)
Purchases of property, plant and equipment and equipment held for lease	(15,979)		(14,537)		(11,708)
Other	(1,496)		(71)		(3,608)
Net cash flows from investing activities	(5,621)		(32,849)		(41,009)
Cash flows from financing activities:
Changes in short term borrowings, net	266		(1,943)		2,079
Acquisition of treasury stock	(4,850)		(1,346)
Other	(497)		(343)		(121)
Net cash flows from financing activities	730		(5,812)		(1,398)
Effects of foreign currency exchange rate changes	25		(140)		248
Increase (decrease) in cash and cash equivalents and restricted cash	33,821		(1,401)		3,569
Cash and cash equivalents and restricted cash at beginning of year	30,811		32,212		28,643
Cash and cash equivalents and restricted cash at end of year	64,632		30,811		32,212
Restricted cash, included in other assets at end of year	$ 457		$ 450		$ 629
Restricted Cash and Cash Equivalents, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssets		us-gaap:OtherAssets		us-gaap:OtherAssets
Insurance and Other [Member]
Cash flows from financing activities:
Proceeds from borrowings	$ 8,144		$ 2,409		$ 2,645
Repayments of borrowings	(5,095)		(7,395)		(5,465)
Cash and cash equivalents at end of year	61,151	[1]	27,749	[1]	28,673
Railroad, Utilities and Energy [Member]
Cash flows from financing activities:
Proceeds from borrowings	5,400		7,019		3,013
Repayments of borrowings	(2,638)		(4,213)		(3,549)
Cash and cash equivalents at end of year	$ 3,024	[1]	$ 2,612	[1]	$ 2,910

[1] Cash and cash equivalents includes U.S. Treasury Bills with maturities of three months or less when purchased of $37.1 billion at December 31, 2019 and $3.9 billion at December 31, 2018.