Insurance (Liabilities for Guarantees) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement In Guaranteed Benefit Liability Gross Rollforward
Balance at January 1,	$ 6,852	$ 5,490	$ 4,528
Incurred guaranteed benefits	1,403	1,422	998
Paid guaranteed benefits	(57)	(60)	(36)
Balance at December 31,	8,198	6,852	5,490
Variable Annuity Guarantees | Guaranteed Minimum Death Benefit
Movement In Guaranteed Benefit Liability Gross Rollforward
Balance at January 1,	1,106	831	619
Incurred guaranteed benefits	367	335	248
Paid guaranteed benefits	(57)	(60)	(36)
Balance at December 31,	1,416	1,106	831
Variable Annuity Guarantees | Guaranteed Minimum Income Benefit
Movement In Guaranteed Benefit Liability Gross Rollforward
Balance at January 1,	2,206	1,872	1,535
Incurred guaranteed benefits	344	334	337
Paid guaranteed benefits	0	0	0
Balance at December 31,	2,550	2,206	1,872
Universal and Variable Life Contracts | Secondary Guarantees
Movement In Guaranteed Benefit Liability Gross Rollforward
Balance at January 1,	3,540	2,787	2,374
Incurred guaranteed benefits	692	753	413
Paid guaranteed benefits	0	0	0
Balance at December 31,	4,232	3,540	2,787
Net Ceded/(Assumed)
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Net	893	1,041	945	$ 799
liabilities for guarantees on long duration contracts reinsurance recoverable incurred benefits net	(93)	151	179
Movement In Guaranteed Benefit Liability Gross Rollforward
Paid guaranteed benefits	(55)	(55)	(33)
Net Ceded/(Assumed) | Secondary Guarantees
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Net	946	1,105	1,007	846
liabilities for guarantees on long duration contracts reinsurance recoverable incurred benefits net	(159)	98	161
Movement In Guaranteed Benefit Liability Gross Rollforward
Paid guaranteed benefits	0	0	0
Net Ceded/(Assumed) | Guaranteed Minimum Death Benefit
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Net	(6)	(45)	(34)	(21)
liabilities for guarantees on long duration contracts reinsurance recoverable incurred benefits net	94	44	20
Movement In Guaranteed Benefit Liability Gross Rollforward
Paid guaranteed benefits	(55)	(55)	(33)
Net Ceded/(Assumed) | Guaranteed Minimum Income Benefit
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Net	(47)	(19)	(28)	(26)
liabilities for guarantees on long duration contracts reinsurance recoverable incurred benefits net	(28)	9	(2)
Movement In Guaranteed Benefit Liability Gross Rollforward
Paid guaranteed benefits	0	0	0
Net
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Net	7,305	5,811	4,545	3,729
Movement In Guaranteed Benefit Liability Gross Rollforward
Incurred guaranteed benefits	1,496	1,271	819
Paid guaranteed benefits	(2)	(5)	(3)
Net | Secondary Guarantees
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Net	3,286	2,435	1,780	1,528
Movement In Guaranteed Benefit Liability Gross Rollforward
Incurred guaranteed benefits	851	655	252
Paid guaranteed benefits	0	0	0
Net | Guaranteed Minimum Death Benefit
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Net	1,422	1,151	865	640
Movement In Guaranteed Benefit Liability Gross Rollforward
Incurred guaranteed benefits	273	291	228
Paid guaranteed benefits	(2)	(5)	(3)
Net | Guaranteed Minimum Income Benefit
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Net	2,597	2,225	1,900	$ 1,561
Movement In Guaranteed Benefit Liability Gross Rollforward
Incurred guaranteed benefits	372	325	339
Paid guaranteed benefits	$ 0	$ 0	$ 0