Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 15,470	$ 15,714	$ 15,201	$ 17,471
Other comprehensive income (loss) before reclassifications, after tax	(352)	(943)	(226)	(2,752)
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	69	104	123	133
Other comprehensive loss	(283)	(839)	(103)	(2,619)
Amounts attributable to noncontrolling interests	31	73	11	260
Change in AOCI	(61)		(61)
Balance at end of period	15,158	14,563	15,158	14,563
Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(507)	(277)	(1,704)
As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		16,221	15,478	19,175
Other comprehensive loss		(1,425)		(4,435)
Effect of Adoption
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period			(277)
Other comprehensive loss		586		1,816
Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(16)	(7)	(7)	(2)
Other comprehensive income (loss) before reclassifications, after tax	(9)		(25)	(5)
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	8	(2)	15	(3)
Other comprehensive loss	(1)	(2)	(10)	(8)
Amounts attributable to noncontrolling interests	1	(1)	1
Change in AOCI
Balance at end of period	(16)	(10)	(16)	(10)
Other comprehensive income (loss) before reclassifications, tax	3	1	7	1
Reclassification of (gains) losses from accumulated other comprehensive income (loss), tax	(2)	0	(4)	1
Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting standards, tax					$ 0	$ 0	$ 0
Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(7)	(7)	(2)
Net Unrealized Gains (Losses) on Other Investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,238)	(1,356)	(2,469)	3,009
Other comprehensive income (loss) before reclassifications, after tax	(1,105)	(1,837)	(880)	(6,721)
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	21	102	53	117
Other comprehensive loss	(1,084)	(1,735)	(827)	(6,604)
Amounts attributable to noncontrolling interests	95	169	69	673
Change in AOCI	(46)		(46)
Balance at end of period	(3,273)	(2,922)	(3,273)	(2,922)
Other comprehensive income (loss) before reclassifications, tax	295	487	235	1,779
Reclassification of (gains) losses from accumulated other comprehensive income (loss), tax	(6)	(11)	(14)	(15)
Net Unrealized Gains (Losses) on Other Investments | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting standards, tax					0	(108)	(617)
Net Unrealized Gains (Losses) on Other Investments | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(1,721)	(2,469)	930
Net Unrealized Gains (Losses) on Other Investments | Effect of Adoption
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		365		2,079
Cumulative impact of changes in discount rates used to measure long duration contracts
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(163)	(768)	(36)	(3,585)
Other comprehensive income (loss) before reclassifications, after tax	818	994	678	4,136
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax
Other comprehensive loss	818	994	678	4,136
Amounts attributable to noncontrolling interests	(69)	(104)	(56)	(429)
Change in AOCI	(1)		(1)
Balance at end of period	585	122	585	122
Other comprehensive income (loss) before reclassifications, tax	(217)	(265)	(180)	(1,100)
Reclassification of (gains) losses from accumulated other comprehensive income (loss), tax	0	0	0	0
Cumulative impact of changes in discount rates used to measure long duration contracts | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting standards, tax					11	228	1,063
Cumulative impact of changes in discount rates used to measure long duration contracts | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		0	0	0
Cumulative impact of changes in discount rates used to measure long duration contracts | Effect of Adoption
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(768)	(36)	(3,585)
Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	20	18	14	(6)
Other comprehensive income (loss) before reclassifications, after tax	(1)	6	5	27
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax		(2)		1
Other comprehensive loss	(1)	4	5	28
Amounts attributable to noncontrolling interests
Change in AOCI
Balance at end of period	19	22	19	22
Other comprehensive income (loss) before reclassifications, tax	(2)	0	(1)	3
Reclassification of (gains) losses from accumulated other comprehensive income (loss), tax	0	(1)	0	0
Unrealized Gains (Losses) on Cash Flow Hedges | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting standards, tax					0	0	0
Unrealized Gains (Losses) on Cash Flow Hedges | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		18	14	(6)
Pension and Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(609)	(625)	(622)	(636)
Other comprehensive income (loss) before reclassifications, after tax
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	40	6	55	18
Other comprehensive loss	40	6	55	18
Amounts attributable to noncontrolling interests	(1)	(1)	(3)	(2)
Change in AOCI	(10)		(10)
Balance at end of period	(580)	(620)	(580)	(620)
Other comprehensive income (loss) before reclassifications, tax	0	0	0	0
Reclassification of (gains) losses from accumulated other comprehensive income (loss), tax	(11)	(2)	(15)	(5)
Pension and Postretirement Benefits | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting standards, tax					0	0	0
Pension and Postretirement Benefits | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(625)	(622)	(636)
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(154)	(175)	(200)	(100)
Other comprehensive income (loss) before reclassifications, after tax	(55)	(106)	(4)	(189)
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax
Other comprehensive loss	(55)	(106)	(4)	(189)
Amounts attributable to noncontrolling interests	5	10		18
Change in AOCI	(4)		(4)
Balance at end of period	(208)	(271)	(208)	(271)
Other comprehensive income (loss) before reclassifications, tax	0	0	0	0
Reclassification of (gains) losses from accumulated other comprehensive income (loss), tax	0	0	0	0
Foreign Currency Translation | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Cumulative effect adjustments from changes in accounting standards, tax					$ 0	$ 0	$ 0
Foreign Currency Translation | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(175)	(200)	(100)
Total Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(3,160)	(2,913)	(3,320)	(1,320)
Balance at end of period	$ (3,473)	(3,679)	(3,473)	(3,679)
Total Accumulated Other Comprehensive Income (Loss) | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(2,510)	(3,284)	186
Total Accumulated Other Comprehensive Income (Loss) | Effect of Adoption
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		$ (403)	$ (36)	$ (1,506)