Investments (excluding Consolidated Investment Entities) - Unrealized Capital Losses 2 (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Unrealized Capital Losses	$ 856		$ 243
Greater than 10%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Credit Enhancement Percentage, minimum	10.00%	10.00%
5% - 10%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Credit Enhancement Percentage, minimum	5.00%	5.00%
Credit Enhancement Percentage, maximum	10.00%	10.00%
0% - 5%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Credit Enhancement Percentage, minimum	0.00%	0.00%
Credit Enhancement Percentage, maximum	5.00%	5.00%
0%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Credit Enhancement Percentage, maximum	0.00%	0.00%
Greater than 100%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Loan to Value Ratio, minimum	100.00%	100.00%
90% - 100%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Loan to Value Ratio, minimum	90.00%	90.00%
Loan to Value Ratio, maximum	100.00%	100.00%
80% - 90%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Loan to Value Ratio, minimum	80.00%	80.00%
Loan to Value Ratio, maximum	90.00%	90.00%
Fair value decline below amortized cost less than 20%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	$ 20,329		6,622
Total Unrealized Capital Losses	766		161
Fair value decline below amortized cost less than 20% | Fixed Rate
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	1,439		1,104
Total Unrealized Capital Losses	49		20
Fair value decline below amortized cost less than 20% | Floating Rate
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	973		378
Total Unrealized Capital Losses	29		12
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Non-Agency | Greater than 10%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	345		162
Total Unrealized Capital Losses	11		2
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Non-Agency | 5% - 10%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	6		11
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Non-Agency | 0% - 5%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	33		25
Total Unrealized Capital Losses	1		1
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Non-Agency | 0%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	16		26
Total Unrealized Capital Losses	1		1
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Non-Agency | Greater than 100%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		0
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Non-Agency | 90% - 100%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		0
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Non-Agency | 80% - 90%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		13
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Non-Agency | Less than 80%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	400		211
Total Unrealized Capital Losses	13		4
Fair value decline below amortized cost less than 20% | Residential mortgage-backed securities, Agency
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	993		878
Total Unrealized Capital Losses	53		26
Fair value decline below amortized cost less than 20% | Other ABS (Non-RMBS)
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	1,019		380
Total Unrealized Capital Losses	12		2
Fair value decline below amortized cost less than 20% | Total RMBS and Other ABS
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	2,412		1,482
Total Unrealized Capital Losses	78		32
Fair value decline below amortized cost greater than 20%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	318		196
Total Unrealized Capital Losses	90		82
Fair value decline below amortized cost greater than 20% | Fixed Rate
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	7		6
Total Unrealized Capital Losses	2		2
Fair value decline below amortized cost greater than 20% | Floating Rate
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	48		8
Total Unrealized Capital Losses	13		3
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Non-Agency | Greater than 10%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		0
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Non-Agency | 5% - 10%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		0
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Non-Agency | 0% - 5%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		1
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Non-Agency | 0%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		0
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Non-Agency | Greater than 100%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		0
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Non-Agency | 90% - 100%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		0
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Non-Agency | 80% - 90%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		0
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Non-Agency | Less than 80%
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	0		1
Total Unrealized Capital Losses	0		0
Fair value decline below amortized cost greater than 20% | Residential mortgage-backed securities, Agency
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	54		12
Total Unrealized Capital Losses	14		4
Fair value decline below amortized cost greater than 20% | Other ABS (Non-RMBS)
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	1		1
Total Unrealized Capital Losses	1		1
Fair value decline below amortized cost greater than 20% | Total RMBS and Other ABS
Available-for-sale Securities, Including Securities Pledged [Line Items]
Total Amortized Cost	55		14
Total Unrealized Capital Losses	$ 15		$ 5