Shareholders' Equity, Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	$ 18,537	$ 19,178	$ 19,181	$ 21,930
Other comprehensive income (loss)	326	1,228	(285)	84
Balance	19,398	18,413	19,398	18,413
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	34	(1,093)	581	(68)
Other comprehensive income (loss) before reclassifications, after tax	341	1,233	(249)	17
Reclassification of (income) losses from accumulated other comprehensive income, after tax	(15)	(5)	(36)	67
Other comprehensive income (loss)	326	1,228	(285)	84
Amounts attributable to noncontrolling interests	(33)	(130)	31	(11)
Balance	327	5	327	5
Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	0	(10)	0	0
Other comprehensive income (loss) before reclassifications, after tax	1	(2)	(2)	(50)
Reclassification of (income) losses from accumulated other comprehensive income, after tax	(1)	4	2	41
Other comprehensive income (loss)	0	2	0	(9)
Amounts attributable to noncontrolling interests				1
Balance	0	(8)	0	(8)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	0	0	1	13
Reclassification of (income) losses from accumulated other comprehensive income, tax	0	(1)	(1)	(11)
Net Unrealized Gains (Losses) on Other Investments [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	1,002	(15)	1,563	918
Other comprehensive income (loss) before reclassifications, after tax	323	1,209	(270)	143
Reclassification of (income) losses from accumulated other comprehensive income, after tax	(23)	(18)	(57)	4
Other comprehensive income (loss)	300	1,191	(327)	147
Amounts attributable to noncontrolling interests	(31)	(126)	35	(15)
Balance	1,271	1,050	1,271	1,050
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	(82)	(321)	72	(34)
Reclassification of (income) losses from accumulated other comprehensive income, tax	7	4	15	(2)
Unrealized Gains (Losses) on Cash Flow Hedges [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(19)	(25)	(23)	(6)
Other comprehensive income (loss) before reclassifications, after tax	8	(1)	11	(20)
Reclassification of (income) losses from accumulated other comprehensive income, after tax		1	1	1
Other comprehensive income (loss)	8	0	12	(19)
Balance	(11)	(25)	(11)	(25)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	(1)	2	(3)	8
Reclassification of (income) losses from accumulated other comprehensive income, tax	(1)	(1)	(2)	(1)
Pension and Postretirement Benefits [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(869)	(842)	(877)	(855)
Other comprehensive income (loss) before reclassifications, after tax	(2)	(2)	(2)	(1)
Reclassification of (income) losses from accumulated other comprehensive income, after tax	9	8	18	21
Other comprehensive income (loss)	7	6	16	20
Amounts attributable to noncontrolling interests	(1)	(1)	(2)	(2)
Balance	(863)	(837)	(863)	(837)
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	(3)	(2)	(5)	(5)
Foreign Currency Translation [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(80)	(201)	(82)	(125)
Other comprehensive income (loss) before reclassifications, after tax	11	29	14	(55)
Other comprehensive income (loss)	11	29	14	(55)
Amounts attributable to noncontrolling interests	(1)	(3)	(2)	5
Balance	(70)	(175)	(70)	(175)
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