Summary of Significant Accounting Policies - Consolidated Statement of Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ 4,847	$ 2,160	$ 3,554
Unrealized net capital gains and losses	1,889	(754)	319
Unrealized foreign currency translation adjustments	(10)	(48)	45
Change in unamortized pension and other postretirement prior service credit	(47)	(59)	(52)
Other comprehensive income (loss), after-tax	1,832	(861)	312
Comprehensive income	6,679	1,299	3,866
Previously reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	4,811	2,252	3,189
Unrealized net capital gains and losses	1,889	(754)	319
Unrealized foreign currency translation adjustments	(4)	(55)	47
Change in unamortized pension and other postretirement prior service credit	141	(144)	307
Other comprehensive income (loss), after-tax	2,026	(953)	673
Comprehensive income	6,837	1,299	3,862
Impact of change | Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	36	(92)	365
Unrealized net capital gains and losses	0	0	0
Unrealized foreign currency translation adjustments	(6)	7	(2)
Change in unamortized pension and other postretirement prior service credit	(188)	85	(359)
Other comprehensive income (loss), after-tax	(194)	92	(361)
Comprehensive income	$ (158)	$ 0	$ 4