Benefit Plans (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Pension benefits
Pension plans' assets
Actual return on plan assets	$ (43)	$ 540
Defined Benefit Plan, Asset Allocation, Derivatives, Minimum	105.00%
Percentage of total plan assets for primary qualified employee				80.00%
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Actual percentage of plan assets				100.00%	100.00%
Notional amount of derivatives, maximum percentage of plan assets	115.00%
Total plan assets at fair value				$ 5,501	$ 5,993
Total plan assets at fair value, allocation (as a percent)	100.00%	100.00%
Securities lending obligation				(167)	(234)
Other net plan assets				19	24
Total reported plan assets	$ 5,783	$ 5,602	$ 5,602	$ 5,353	5,783
Pension plan assets
Fair value of plan assets, beginning of year	5,783	5,602
Fair value of plan assets, end of year	$ 5,353	$ 5,783	$ 5,602
Expected weighted average long-term rate of return on plan assets (as a percent)	7.33%	7.36%	7.75%
Expected weighted average long-term rate of return on plan assets for the next fiscal year (as a percent)	7.30%
Expected weighted average long-term rate of return on primary employee plan assets for the next fiscal year (as a percent)	7.75%
Expected weighted average long-term rate of return on employee-agent plan assets for the next fiscal year (as a percent)	5.75%
Arithmetic average of the annual actual return on plan assets for the last 10 years (as a percent)				6.90%
Arithmetic average of the annual actual return on plan assets for the last 5 years (as a percent)				7.70%
Cash flows
Defined benefit pension plans, estimated employer contributions in next fiscal year	$ 129
Employer contribution	125	$ 49
Participant contributions	$ 0	$ 1
Estimated future benefit payments
2016				$ 341
2017				372
2018				388
2019				436
2020				472
2021-2025				2,569
Total benefit payments				4,578
Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				342	1,116
Total plan assets at fair value, allocation (as a percent)	6.20%	18.60%
Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				4,668	4,372
Total plan assets at fair value, allocation (as a percent)	84.90%	73.00%
Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				491	505
Total plan assets at fair value, allocation (as a percent)	8.90%	8.40%
Total reported plan assets	$ 505	$ 690	$ 946	491	505
Pension plan assets
Fair value of plan assets, beginning of year	505	690	946
Actual return on plan assets: Relating to assets sold during the period	1	(5)	15
Actual return on plan assets: Relating to assets still held at the reporting date	(24)	12	28
Purchases, sales and settlements, net	11	(192)	(299)
Net transfers in and/or (out) of Level 3	(2)	0	0
Fair value of plan assets, end of year	491	505	690
Postretirement benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total reported plan assets	0	0		0	$ 0
Pension plan assets
Fair value of plan assets, beginning of year	0
Fair value of plan assets, end of year	0	0
Cash flows
Employer contribution	35	38
Participant contributions	$ 19	19
Estimated future benefit payments
2016				26
2017				26
2018				26
2019				28
2020				29
2021-2025				155
Total benefit payments				$ 290
Equity securities | Pension benefits
Pension plans' assets
Percent of total equity securities in primary qualified employee plan	86.00%
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	53.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	63.00%
Actual percentage of plan assets				60.00%	41.00%
Total plan assets at fair value				$ 3,181	$ 2,345
Equity securities | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				136	161
Equity securities | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				2,945	2,109
Equity securities | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				100	75
Total reported plan assets	$ 75	237	314	$ 100	$ 75
Pension plan assets
Fair value of plan assets, beginning of year	75	237	314
Actual return on plan assets: Relating to assets sold during the period	1	2	3
Actual return on plan assets: Relating to assets still held at the reporting date	(5)	2	18
Purchases, sales and settlements, net	29	(166)	(98)
Net transfers in and/or (out) of Level 3	0	0	0
Fair value of plan assets, end of year	$ 100	75	237
Fixed income securities | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	28.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	37.00%
Actual percentage of plan assets				30.00%	50.00%
Cash collateral from target asset allocation, investment allocation (as a percent)	5.00%
U.S. government and agencies | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				$ 406	$ 914
U.S. government and agencies | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				72	870
U.S. government and agencies | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				334	44
U.S. government and agencies | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Foreign government | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					28
Foreign government | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					0
Foreign government | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					28
Foreign government | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					0
Municipal | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				7	14
Municipal | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Municipal | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Municipal | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				7	14
Total reported plan assets	$ 14	18	129	7	14
Pension plan assets
Fair value of plan assets, beginning of year	14	18	129
Actual return on plan assets: Relating to assets sold during the period	0	0	7
Actual return on plan assets: Relating to assets still held at the reporting date	0	0	1
Purchases, sales and settlements, net	(7)	(4)	(119)
Net transfers in and/or (out) of Level 3	0	0	0
Fair value of plan assets, end of year	7	14	18
Corporate | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				1,215	1,834
Corporate | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Corporate | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				1,205	1,822
Corporate | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				10	12
Total reported plan assets	12	18	10	10	12
Pension plan assets
Fair value of plan assets, beginning of year	12	18	10
Actual return on plan assets: Relating to assets sold during the period	0	0	5
Actual return on plan assets: Relating to assets still held at the reporting date	0	0	0
Purchases, sales and settlements, net	0	(6)	3
Net transfers in and/or (out) of Level 3	(2)	0	0
Fair value of plan assets, end of year	$ 10	12	18
RMBS | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					115
RMBS | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					0
RMBS | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					115
RMBS | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					0
Securities Pledged as Collateral [Member] | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Defined Benefit Plan, Assets for Plan Benefits				$ 152	$ 217
Limited partnership interests | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	0.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	12.00%
Actual percentage of plan assets				7.00%	7.00%
Short-term investments | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Cash collateral from target asset allocation, investment allocation (as a percent)	95.00%
Total plan assets at fair value				$ 296	$ 309
Short-term investments | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				112	55
Short-term investments | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				184	254
Short-term investments | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				$ 0	$ 0
Short-term investments and other | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Target asset allocation	0.00%
Actual percentage of plan assets				3.00%	2.00%
Real estate funds | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				$ 104	$ 154
Real estate funds | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Real estate funds | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Real estate funds | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				104	154
Total reported plan assets	$ 154	197	214	104	154
Pension plan assets
Fair value of plan assets, beginning of year	154	197	214
Actual return on plan assets: Relating to assets sold during the period	0	(3)	0
Actual return on plan assets: Relating to assets still held at the reporting date	(12)	6	11
Purchases, sales and settlements, net	(38)	(46)	(28)
Net transfers in and/or (out) of Level 3	0	0	0
Fair value of plan assets, end of year	104	154	197
Private equity funds | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				237	218
Private equity funds | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Private equity funds | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Private equity funds | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				237	218
Total reported plan assets	218	211	199	237	218
Pension plan assets
Fair value of plan assets, beginning of year	218	211	199
Actual return on plan assets: Relating to assets sold during the period	0	(4)	0
Actual return on plan assets: Relating to assets still held at the reporting date	(8)	4	(2)
Purchases, sales and settlements, net	27	7	14
Net transfers in and/or (out) of Level 3	0	0	0
Fair value of plan assets, end of year	237	218	211
Hedge funds | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				33	32
Hedge funds | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Hedge funds | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Hedge funds | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				33	32
Total reported plan assets	32	9	80	33	32
Pension plan assets
Fair value of plan assets, beginning of year	32	9	80
Actual return on plan assets: Relating to assets sold during the period	0	0	0
Actual return on plan assets: Relating to assets still held at the reporting date	1	0	0
Purchases, sales and settlements, net	0	23	(71)
Net transfers in and/or (out) of Level 3	0	0	0
Fair value of plan assets, end of year	$ 33	$ 32	$ 9
Cash and cash equivalents | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				22	34
Cash and cash equivalents | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				22	34
Cash and cash equivalents | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				0	0
Cash and cash equivalents | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value				$ 0	0
Free Standing Derivative Assets | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					(1)
Free Standing Derivative Assets | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					(1)
Free Standing Derivative Assets | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					0
Free Standing Derivative Assets | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					0
Free Standing Derivatives Liabilities | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					(3)
Free Standing Derivatives Liabilities | Pension benefits | Quoted prices in active markets for identical assets (Level 1)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					(3)
Free Standing Derivatives Liabilities | Pension benefits | Significant other observable inputs (Level 2)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					0
Free Standing Derivatives Liabilities | Pension benefits | Significant unobservable inputs (Level 3)
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Total plan assets at fair value					$ 0
Equity securities | Fixed income securities | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Actual percentage of plan assets				3.00%	3.00%
Equity securities | Derivatives | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Actual percentage of plan assets					9.00%
Equity securities | Private equity funds | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Actual percentage of plan assets				2.00%	1.00%