Investments (Credit Quality of Commercial Mortgage Loans) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 83,270	$ 80,635
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	3,083
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	9,156
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	8,761
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	6,717
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	6,508
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	14,094
Financing Receivable, Revolving	2,724
Mortgage Loans, Gross	$ 51,043	$ 49,624
Loans Receivable Commercial Mortgage Percentage	100.00%
Commercial Mortgage Loans | Less than 65%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 2,353
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	5,910
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	6,642
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	4,549
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	5,307
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	11,489
Financing Receivable, Revolving	2,724
Mortgage Loans, Gross	$ 38,974
Loans Receivable Commercial Mortgage Percentage	76.40%
Commercial Mortgage Loans | 65% to 75%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 704
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,095
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,896
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,448
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	767
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,507
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 9,417
Loans Receivable Commercial Mortgage Percentage	18.40%
Commercial Mortgage Loans | 76% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 2
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	124
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	267
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	301
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	185
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 879
Loans Receivable Commercial Mortgage Percentage	1.70%
Commercial Mortgage Loans | Greater than 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 24
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	27
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	223
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	453
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	133
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	913
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 1,773
Loans Receivable Commercial Mortgage Percentage	3.50%
Commercial Mortgage Loans | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 2,980
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	8,558
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	8,342
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	6,193
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	6,188
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	12,997
Financing Receivable, Revolving	2,724
Mortgage Loans, Gross	$ 47,982
Loans Receivable Commercial Mortgage Percentage	94.00%
Commercial Mortgage Loans | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	82
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	113
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	122
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	320
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	902
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 1,539
Loans Receivable Commercial Mortgage Percentage	3.00%
Commercial Mortgage Loans | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 103
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	516
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	306
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	402
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	195
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 1,522
Loans Receivable Commercial Mortgage Percentage	3.00%