Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2022
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 16,525	$ 15,201
Other comprehensive income (loss) before reclassifications, after tax	70	262
Reclassification of losses from accumulated other comprehensive loss, after tax	31	27
Other comprehensive income (loss)	101	289
Amounts attributable to noncontrolling interests	(8)	(31)
Other	3
Balance at end of period	16,998	15,314
Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(277)
As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		15,478
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	(12)	(7)
Other comprehensive income (loss) before reclassifications, after tax	(1)	(8)
Reclassification of losses from accumulated other comprehensive loss, after tax	3
Other comprehensive income (loss)	2	(8)
Amounts attributable to noncontrolling interests		1
Other	1
Balance at end of period	(9)	(14)
Other comprehensive income (loss) before reclassifications, tax	0	2
Reclassification of losses from accumulated other comprehensive loss, tax	(1)	0
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]
Balance at beginning of period
Cumulative effect adjustments from changes in accounting standards, tax			$ 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)
Net Unrealized Gains (Losses) on Other Investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(1,483)	(2,469)
Other comprehensive income (loss) before reclassifications, after tax	(239)	652
Reclassification of losses from accumulated other comprehensive loss, after tax	22	18
Other comprehensive income (loss)	(217)	670
Amounts attributable to noncontrolling interests	19	(68)
Other	5
Balance at end of period	(1,676)	(1,867)
Other comprehensive income (loss) before reclassifications, tax	64	(176)
Reclassification of losses from accumulated other comprehensive loss, tax	(6)	(4)
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]
Balance at beginning of period
Cumulative effect adjustments from changes in accounting standards, tax			0
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		(2,469)
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	(329)	(36)
Other comprehensive income (loss) before reclassifications, after tax	341	(396)
Reclassification of losses from accumulated other comprehensive loss, after tax
Other comprehensive income (loss)	341	(396)
Amounts attributable to noncontrolling interests	(29)	39
Other
Balance at end of period	(17)	(393)
Other comprehensive income (loss) before reclassifications, tax	(91)	105
Reclassification of losses from accumulated other comprehensive loss, tax	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]
Balance at beginning of period		(36)
Cumulative effect adjustments from changes in accounting standards, tax			11
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
Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	9	14
Other comprehensive income (loss) before reclassifications, after tax	2	(2)
Reclassification of losses from accumulated other comprehensive loss, after tax
Other comprehensive income (loss)	2	(2)
Amounts attributable to noncontrolling interests
Other	(1)
Balance at end of period	10	12
Other comprehensive income (loss) before reclassifications, tax	(1)	1
Reclassification of losses from accumulated other comprehensive loss, tax	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]
Balance at beginning of period
Cumulative effect adjustments from changes in accounting standards, tax			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		14
Pension and Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(533)	(622)
Other comprehensive income (loss) before reclassifications, after tax
Reclassification of losses from accumulated other comprehensive loss, after tax	6	9
Other comprehensive income (loss)	6	9
Amounts attributable to noncontrolling interests	(1)	(1)
Other	(2)
Balance at end of period	(530)	(614)
Other comprehensive income (loss) before reclassifications, tax	0	0
Reclassification of losses from accumulated other comprehensive loss, tax	(1)	(2)
Pension and Postretirement Benefits | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period
Cumulative effect adjustments from changes in accounting standards, tax			0
Pension and Postretirement Benefits | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(622)
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(149)	(200)
Other comprehensive income (loss) before reclassifications, after tax	(33)	16
Reclassification of losses from accumulated other comprehensive loss, after tax
Other comprehensive income (loss)	(33)	16
Amounts attributable to noncontrolling interests	3	(2)
Other
Balance at end of period	(179)	(186)
Other comprehensive income (loss) before reclassifications, tax	0	0
Reclassification of losses from accumulated other comprehensive loss, tax	0	0
Foreign Currency Translation | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period
Cumulative effect adjustments from changes in accounting standards, tax			$ 0
Foreign Currency Translation | As Reported
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(200)
Total Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,497)	(3,320)
Balance at end of period	$ (2,401)	(3,062)
Total Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period		(36)
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		$ (3,284)