Investments (Credit Quality of Commercial Mortgage Loans) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 66,378	$ 65,591
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	2,899
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	5,575
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	6,013
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	4,860
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	4,899
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	11,410
Financing Receivable, Revolving	2,468
Mortgage Loans, Gross	$ 38,124	$ 37,311
Loans Receivable Commercial Mortgage Percentage	100.00%
Commercial Mortgage Loans | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 2,575
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	5,160
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	5,826
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	4,348
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	4,707
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	10,554
Financing Receivable, Revolving	2,468
Mortgage Loans, Gross	$ 35,638
Loans Receivable Commercial Mortgage Percentage	93.50%
Commercial Mortgage Loans | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 213
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	18
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	68
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	192
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	735
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 1,226
Loans Receivable Commercial Mortgage Percentage	3.20%
Commercial Mortgage Loans | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 111
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	415
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	169
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	444
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	121
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 1,260
Loans Receivable Commercial Mortgage Percentage	3.30%
Commercial Mortgage Loans | Less than 65%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 2,210
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,512
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	4,418
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	3,033
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	3,975
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	9,196
Financing Receivable, Revolving	2,468
Mortgage Loans, Gross	$ 28,812
Loans Receivable Commercial Mortgage Percentage	75.60%
Commercial Mortgage Loans | 65% to 75%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 689
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,939
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,410
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,112
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	632
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,314
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 7,096
Loans Receivable Commercial Mortgage Percentage	18.60%
Commercial Mortgage Loans | 76% to 80%
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	124
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	264
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	190
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	185
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 763
Loans Receivable Commercial Mortgage Percentage	2.00%
Commercial Mortgage Loans | Greater than 80%
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	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	185
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	451
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	102
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	715
Financing Receivable, Revolving	0
Mortgage Loans, Gross	$ 1,453
Loans Receivable Commercial Mortgage Percentage	3.80%