Summary of Significant Accounting Policies - Consolidated Statements of Shareholders' Equity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	$ 21,312	$ 22,551
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)
Balance, end of year	25,998	21,312	22,551
Retained income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	44,033	41,579	39,009
Cumulative effect of change in accounting principle				$ 21	$ 1,088	$ 0
Net income	4,847	2,160	3,554
Dividends, Common Stock, Cash	(658)	(646)	(540)
Dividends on preferred stock	(169)	(148)	(116)
Reclassification of tax effects due to change in accounting principle	0	0	(328)
Balance, end of year	48,074	44,033	41,579
Accumulated other comprehensive income (loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	118	1,889	1,249
Cumulative effect of change in accounting principle			(910)	0	(910)	$ 0
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)
Reclassification of tax effects due to change in accounting principle	0	0	328
Balance, end of year	1,950	118	1,889
Previously reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	21,312
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
Balance, end of year	26,156	21,312
Previously reported | Retained income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	45,708	43,162	40,678
Cumulative effect of change in accounting principle				21	1,088
Net income	4,811	2,252	3,189
Dividends, Common Stock, Cash	(658)	(646)	(540)
Dividends on preferred stock	(169)	(148)	(116)
Reclassification of tax effects due to change in accounting principle			(49)
Balance, end of year	49,713	45,708	43,162
Previously reported | Accumulated other comprehensive income (loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	(1,557)	306	(416)
Cumulative effect of change in accounting principle				0	(910)
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
Reclassification of tax effects due to change in accounting principle			49
Balance, end of year	469	(1,557)	306
Impact of change | Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	0
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)
Balance, end of year	(158)	0
Impact of change | Impact of change | Retained income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	(1,675)	(1,583)	(1,669)
Cumulative effect of change in accounting principle				0	0
Net income	36	(92)	365
Dividends, Common Stock, Cash	0	0	0
Dividends on preferred stock	0	0	0
Reclassification of tax effects due to change in accounting principle			(279)
Balance, end of year	(1,639)	(1,675)	(1,583)
Impact of change | Impact of change | Accumulated other comprehensive income (loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Balance, beginning of year	1,675	1,583	1,665
Cumulative effect of change in accounting principle				$ 0	$ 0
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)
Reclassification of tax effects due to change in accounting principle			279
Balance, end of year	$ 1,481	$ 1,675	$ 1,583