Shareholders' Equity - Progression of the components of accumulated other comprehensive income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance	$ 1,273
Other comprehensive loss, net of tax	(306)	$ (829)
Reclassify AOCI	1,273
AOCI ending balance	967
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, Pretax	(355)	(1,095)
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, tax	74	230
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, net of tax	(281)	(865)
Reclassification from accumulated other comprehensive income, pretax	(14)	24
Reclassification from accumulated other comprehensive income, tax	3	(5)
Reclassification from accumulated other comprehensive income, net of tax	(11)	19
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax	(369)	(1,071)
Other comprehensive income (loss), tax	77	225
Other comprehensive loss, net of tax	(292)	(846)
Accumulated Net Investment Gain (Loss) Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, net of tax	0	0
Reclassification from accumulated other comprehensive income, net of tax	0	0
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive loss, net of tax	0	0
Accumulated Net Investment Gain (Loss) Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), unrealized holding gains on securities arising during the period, net of tax	(281)	(865)
Reclassification from accumulated other comprehensive income, net of tax	(11)	19
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance	1,255	862
Other comprehensive loss, net of tax	(292)	(846)
Reclassify AOCI	963	16
AOCI ending balance	963	16
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax	(17)	34
Other comprehensive income (loss), tax	3	(7)
Other comprehensive loss, net of tax	(14)	27
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive loss, net of tax	0	0
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance	41	17
Other comprehensive loss, net of tax	(14)	27
Reclassify AOCI	27	44
AOCI ending balance	27	44
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax	0	(10)
Other comprehensive income (loss), tax	0	0
Other comprehensive loss, net of tax	0	(10)
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive loss, net of tax	0	(2)
Accumulated Foreign Currency Adjustment Attributable to Parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance	(16)	(9)
Other comprehensive loss, net of tax	0	(12)
Reclassify AOCI	(16)	(21)
AOCI ending balance	(16)	(21)
Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax	0	0
Other comprehensive income (loss), tax	0	0
Other comprehensive loss, net of tax	0	0
Accumulated Defined Benefit Plans Adjustment Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive loss, net of tax	0	0
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance	(7)	(7)
Other comprehensive loss, net of tax	0	0
Reclassify AOCI	(7)	(7)
AOCI ending balance	(7)	(7)
AOCI Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), pretax	(386)	(1,047)
Other comprehensive income (loss), tax	80	218
Other comprehensive loss, net of tax	(306)	(829)
AOCI Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive loss, net of tax	0	(2)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income [Roll Forward]
AOCI beginning balance	1,273	863
Other comprehensive loss, net of tax	(306)	(831)
Reclassify AOCI	967	32
AOCI ending balance	$ 967	$ 32