Benefit Plans (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension benefits
Pension plans' assets
Percentage of total plan assets for primary qualified employee	79.00%
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%
Total plan assets at fair value	$ 5,993	$ 5,802
Total plan assets at fair value, allocation (as a percent)	100.00%	100.00%
Securities lending obligation	(234)	(290)
Other net plan assets	24	90
Total reported plan assets	5,783	5,602	5,398
Pension plan assets
Fair value of plan assets, beginning of year	5,602	5,398
Fair value of plan assets, end of year	5,783	5,602	5,398
Expected weighted average long-term rate of return on plan assets (as a percent)	7.36%	7.75%	8.50%
Expected weighted average long-term rate of return on plan assets for the next fiscal year (as a percent)	7.33%
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)	8.00%
Arithmetic average of the annual actual return on plan assets for the last 5 years (as a percent)	10.30%
Cash flows
Defined benefit pension plans, estimated employer contributions in next fiscal year	127
Employer contribution	49	561
Participant contributions	1	1
Estimated future benefit payments
2015	368
2016	392
2017	434
2018	449
2019	495
2020-2024	2,608
Total benefit payments	4,746
Pension benefits | Minimum
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Notional amount of derivatives, maximum percentage of plan assets	105.00%
Pension benefits | Maximum
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Notional amount of derivatives, maximum percentage of plan assets	115.00%
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	1,116	847
Total plan assets at fair value, allocation (as a percent)	18.60%	14.60%
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	4,372	4,265
Total plan assets at fair value, allocation (as a percent)	73.00%	73.50%
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	505	690
Total plan assets at fair value, allocation (as a percent)	8.40%	11.90%
Total reported plan assets	505	690	946
Pension plan assets
Fair value of plan assets, beginning of year	690	946	938
Actual return on plan assets: Relating to assets sold during the period	(5)	15	30
Actual return on plan assets: Relating to assets still held at the reporting date	12	28	3
Purchases, sales and settlements, net	(192)	(299)	(25)
Fair value of plan assets, end of year	505	690	946
Postretirement benefits
Cash flows
Employer contribution	38	39
Participant contributions	19	18
Estimated future benefit payments
2015	39
2016	31
2017	33
2018	34
2019	37
2020-2024	204
Total benefit payments	378
Equity securities | Pension benefits
Pension plans' assets
Percent of total equity securities in primary qualified employee plan	81.00%
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Target asset allocation, minimum range (as a percent)	40.00%
Target asset allocation, maximum range (as a percent)	50.00%
Actual percentage of plan assets	41.00%	49.00%
Total plan assets at fair value	2,345	2,703
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	161	160
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	2,109	2,306
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	75	237
Total reported plan assets	75	237	314
Pension plan assets
Fair value of plan assets, beginning of year	237	314	309
Actual return on plan assets: Relating to assets sold during the period	2	3
Actual return on plan assets: Relating to assets still held at the reporting date	2	18	8
Purchases, sales and settlements, net	(166)	(98)	(3)
Fair value of plan assets, end of year	75	237	314
Fixed income securities | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Target asset allocation, minimum range (as a percent)	43.00%
Target asset allocation, maximum range (as a percent)	52.00%
Actual percentage of plan assets	50.00%	41.00%
Cash collateral from target asset allocation, investment allocation (as a percent)	6.00%
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	914	660
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	870	608
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	44	52
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	44
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	44
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	14	18
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	14	18
Total reported plan assets	14	18	129
Pension plan assets
Fair value of plan assets, beginning of year	18	129	163
Actual return on plan assets: Relating to assets sold during the period		7	5
Actual return on plan assets: Relating to assets still held at the reporting date		1	(2)
Purchases, sales and settlements, net	(4)	(119)	(37)
Fair value of plan assets, end of year	14	18	129
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	1,834	1,451
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	1,822	1,433
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	12	18
Total reported plan assets	12	18	10
Pension plan assets
Fair value of plan assets, beginning of year	18	10	9
Actual return on plan assets: Relating to assets sold during the period		5	1
Purchases, sales and settlements, net	(6)	3
Fair value of plan assets, end of year	12	18	10
Residential mortgage-backed securities ("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	83
Residential mortgage-backed securities ("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	83
Limited partnership interests | Pension benefits
Pension plans' weighted average target percentage of plan assets and the actual percentage of plan assets
Target asset allocation, minimum range (as a percent)	0.00%
Target asset allocation, maximum range (as a percent)	18.00%
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)	94.00%
Total plan assets at fair value	309	398
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	55	54
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	254	344
Short-term investments and other | 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%	3.00%
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	154	197
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	154	197
Total reported plan assets	154	197	214
Pension plan assets
Fair value of plan assets, beginning of year	197	214	192
Actual return on plan assets: Relating to assets sold during the period	(3)		16
Actual return on plan assets: Relating to assets still held at the reporting date	6	11	2
Purchases, sales and settlements, net	(46)	(28)	4
Fair value of plan assets, end of year	154	197	214
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	218	211
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	218	211
Total reported plan assets	218	211	199
Pension plan assets
Fair value of plan assets, beginning of year	211	199	186
Actual return on plan assets: Relating to assets sold during the period	(4)		8
Actual return on plan assets: Relating to assets still held at the reporting date	4	(2)	(6)
Purchases, sales and settlements, net	7	14	11
Fair value of plan assets, end of year	218	211	199
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	32	9
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	32	9
Total reported plan assets	32	9	80
Pension plan assets
Fair value of plan assets, beginning of year	9	80	79
Actual return on plan assets: Relating to assets still held at the reporting date			1
Purchases, sales and settlements, net	23	(71)
Fair value of plan assets, end of year	32	9	80
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	34	25
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	34	25
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)	4
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)	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		3
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)	(1)
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)	$ (1)