Shareholders' Equity (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	$ 19,178	$ 21,902		$ 21,930		$ 21,386
Other comprehensive income (loss)	1,228	440		84		989
Balance	18,413	22,394		$ 18,413		$ 22,394
Treasury Stock [Abstract]
Treasury stock repurchased (in shares)				10.7		9.8
Purchase of treasury stock	33	151		$ 478		$ 473
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(1,093)	(390)	[1]	(68)	[1]	(880)	[1]
Other comprehensive income (loss) before reclassifications, after tax	1,233	430		17		965
Reclassification of (income) losses from accumulated other comprehensive income, after tax	(5)	10		67		24
Other comprehensive income (loss)	1,228	440		84		989
Amounts attributable to noncontrolling interests	(130)	(47)		(11)		(106)
Balance	5	3		5		3
Net Unrealized Gains (Losses) on Investments OTTI Losses [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(10)	18	[1]	0	[1]	14	[1]
Other comprehensive income (loss) before reclassifications, after tax	(2)	(1)		(50)		3
Reclassification of (income) losses from accumulated other comprehensive income, after tax	4	1		41		1
Other comprehensive income (loss)	2	0		(9)		4
Amounts attributable to noncontrolling interests				1
Balance	(8)	18		(8)		18
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	0	(1)		13		(2)
Reclassification of (income) losses from accumulated other comprehensive income, tax	(1)	0		(11)		0
Net Unrealized Gains (Losses) on Other Investments [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(15)	527	[1]	918	[1]	57	[1]
Other comprehensive income (loss) before reclassifications, after tax	1,209	434		143		955
Reclassification of (income) losses from accumulated other comprehensive income, after tax	(18)	2		4		7
Other comprehensive income (loss)	1,191	436		147		962
Amounts attributable to noncontrolling interests	(126)	(46)		(15)		(102)
Balance	1,050	917		1,050		917
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	(321)	(114)		(34)		(254)
Reclassification of (income) losses from accumulated other comprehensive income, tax	4	0		(2)		(1)
Unrealized Gains (Losses) on Cash Flow Hedges [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(25)	(1)	[1]	(6)	[1]	5	[1]
Other comprehensive income (loss) before reclassifications, after tax	(1)	(6)		(20)		(12)
Reclassification of (income) losses from accumulated other comprehensive income, after tax	1			1
Other comprehensive income (loss)	0	(6)		(19)		(12)
Balance	(25)	(7)		(25)		(7)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	2	2		8		4
Reclassification of (income) losses from accumulated other comprehensive income, tax	(1)	0		(1)		0
Pension and Postretirement Benefits [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(842)	(786)	[1]	(855)	[1]	(793)	[1]
Other comprehensive income (loss) before reclassifications, after tax	(2)			(1)		(1)
Reclassification of (income) losses from accumulated other comprehensive income, after tax	8	7		21		16
Other comprehensive income (loss)	6	7		20		15
Amounts attributable to noncontrolling interests	(1)	(1)		(2)		(2)
Balance	(837)	(780)		(837)		(780)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	0	0		0		0
Reclassification of (income) losses from accumulated other comprehensive income, tax	(2)	(3)		(5)		(5)
Foreign Currency Translation [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(201)	(148)	[1]	(125)	[1]	(163)	[1]
Other comprehensive income (loss) before reclassifications, after tax	29	3		(55)		20
Other comprehensive income (loss)	29	3		(55)		20
Amounts attributable to noncontrolling interests	(3)			5		(2)
Balance	(175)	(145)		(175)		(145)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	0	0		0		0
Reclassification of (income) losses from accumulated other comprehensive income, tax	$ 0	$ 0		0		$ 0
Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance				$ 21,925

[1] On January 1, 2020, the Company adopted ASU 2016-13; see Note 1. The Net Unrealized Gains (Losses) on Investments with OTTI Losses column that tracked the change in unrealized gains (losses) on investments with OTTI losses has been replaced with the Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses column. The balance as of January 1, 2020 in the Net Unrealized Gains (Losses) on Investments with OTTI Losses column is now reported in the Net Unrealized Gains (Losses) on Other Investments column. Prior period amounts were not adjusted for the adoption of this standard.