Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Cash flows from operating activities:
Net earnings	$ 43,253		$ 81,792		$ 4,322
Adjustments to reconcile net earnings to operating cash flows:
Investment (gains) losses	(40,905)		(71,123)		22,155
Depreciation and amortization	10,596		10,064		9,779
Other, including asset impairment charges	11,263		(1,254)		2,957
Changes in operating assets and liabilities:
Losses and loss adjustment expenses	4,819		6,087		3,449
Deferred charges reinsurance assumed	1,307		357		1,174
Unearned premiums	1,587		1,707		1,794
Receivables and originated loans	(1,609)		(2,303)		(3,443)
Other assets	(1,109)		(2,011)		(1,832)
Other liabilities	3,376		190		2,002
Income taxes	7,195		15,181		(4,957)
Net cash flows from operating activities	39,773		38,687		37,400
Cash flows from investing activities:
Purchases of equity securities	(30,161)		(18,642)		(43,210)
Sales of equity securities	38,756		14,336		18,783
Purchases of U.S. Treasury Bills and fixed maturity securities	(208,429)		(136,123)		(141,844)
Sales of U.S. Treasury Bills and fixed maturity securities	31,873		15,929		39,693
Redemptions and maturities of U.S. Treasury Bills and fixed maturity securities	149,709		137,767		113,045
Purchases of loans and finance receivables	(772)		(75)		(1,771)
Collections of loans and finance receivables	393		345		342
Acquisitions of businesses, net of cash acquired	(2,532)		(1,683)		(3,279)
Purchases of property, plant and equipment and equipment held for lease	(13,012)		(15,979)		(14,537)
Other	(3,582)		(1,496)		(71)
Net cash flows from investing activities	(37,757)		(5,621)		(32,849)
Cash flows from financing activities:
Changes in short term borrowings, net	(1,118)		266		(1,943)
Acquisition of treasury stock	(24,706)		(4,850)		(1,346)
Other	(429)		(497)		(343)
Net cash flows from financing activities	(18,344)		730		(5,812)
Effects of foreign currency exchange rate changes	92		25		(140)
Increase (decrease) in cash and cash equivalents and restricted cash	(16,236)		33,821		(1,401)
Cash and cash equivalents and restricted cash at beginning of year	64,632		30,811		32,212
Cash and cash equivalents and restricted cash at end of year	48,396		64,632		30,811
Restricted cash, included in other assets at end of year	$ 406		$ 457		$ 450
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	$ 5,925		$ 8,144		$ 2,409
Repayments of borrowings	(2,700)		(5,095)		(7,395)
Cash and cash equivalents at end of year	44,714	[1]	61,151	[1]	27,749
Railroad, Utilities and Energy [Member]
Cash flows from financing activities:
Proceeds from borrowings	8,445		5,400		7,019
Repayments of borrowings	(3,761)		(2,638)		(4,213)
Cash and cash equivalents at end of year	$ 3,276	[1]	$ 3,024	[1]	$ 2,612

[1] Includes U.S. Treasury Bills with maturities of three months or less when purchased of $23.2 billion at December 31, 2020 and $37.1 billion at December 31, 2019.